Building a Bastion Host Using HP-UX 11

by Kevin Steves [Published on 16 Oct. 2002 / Last Updated on 23 Jan. 2013]

Very good paper. Almost FAQ.

This is an update to a paper I originally wrote in 1997 titled "Building a Bastion Host Using HP-UX 10". It has been modified to reflect changes in HP-UX 11, in addition to incorporating the changes in my methodology that have occurred over the last 3 years.

A bastion host is a computer system that is exposed to attack, and may be a critical component in a network security system. Special attention must be paid to these highly fortified hosts, both during initial construction and ongoing operation. Bastion hosts can include:

  • Firewall gateways
  • Web servers
  • FTP servers
  • Name servers (DNS)
  • Mail hubs
  • Victim hosts (sacrificial lambs)
This paper presents a methodology for building a bastion host using HP-UX 11, and walks through the steps used to build a sample, generic bastion host using HP-UX 11.00. While the principles and procedures can be applied to other HP-UX versions as well as other Unix variants, our focus is on HP-UX 11.

What is a Bastion Host?

The American Heritage Dictionary defines a bastion as:

1. A projecting part of a rampart or other fortification. 2. A well-fortified position or area. 3. Something regarded as a defensive stronghold.
Marcus Ranum is generally credited with applying the term bastion to hosts that are exposed to attack, and its common use in the firewall community. In [1] he says:

Bastions are the highly fortified parts of a medieval castle; points that overlook critical areas of defense, usually having stronger walls, room for extra troops, and the occasional useful tub of boiling hot oil for discouraging attackers. A bastion host is a system identified by the firewall administrator as a critical strong point in the network's security. Generally, bastion hosts will have some degree of extra attention paid to their security, may undergo regular audits, and may have modified software.
Bastion hosts are not general purpose computing resources. They differ in both their purpose and their specific configuration. A victim host may permit network logins so users can run untrusted services, while a firewall gateway may only permit logins at the system console. The process of configuring or constructing a bastion host is often referred to as hardening.

The effectiveness of a specific bastion host configuration can usually be judged by answering the following questions:

  1. How does the bastion host protect itself from attack?
  2. How does the bastion host protect the network behind it from attack?
Extreme caution should be exercised when installing new software on bastion hosts. Very few software products have been designed and tested to run on these exposed systems.

See [2] for a thorough treatment of bastion hosts.

Methodology

Let's begin by creating a methodology. These are the principles and procedures we will follow as we build bastion hosts. Included in this is our mindset, which will help guide the configuration decisions we make.

We take a paranoid stance--what we don't know can hurt us, and what we think we know we may not trust. We start with a clean operating system install. If subsystems are not needed for the applications we plan to run on the bastion host, we will not install them in the first place, or disable or remove them after the install. Next we install any additional operating system software needed on the bastion host, such as network drivers not available on the install media or the LVM Mirror product, followed by the latest patch bundle (Support Plus Bundle). We perform a security patch review and install HP-UX security patches that apply to our installed software configuration. The system is configured with commercial security (as a trusted system) which removes the hashed passwords from the /etc/passwd file and provides other useful security features such as auditing and login passwords with lengths greater than 8 characters. Unneeded pseudo-accounts in the password database are removed. We remove the set-id bits from all programs then selectively add them back to programs that must be run by non-privileged users. This proactive approach may save us time and a future vulnerability window when the next security defect is discovered in a set-id program. We tighten up the world-write permissions on system files, and set the sticky bit on publicly writable directories. We next set a number of tunable network parameters with a paranoid stance toward security. At this point, the applications that will run on the bastion host can be installed, configured and tested. This may include installing additional security software, such as TCP wrappers and SSH. After testing is complete, we create a bootable System Recovery Tape of the root volume group.

Sample Blueprint

Now let's lay out the blueprint that we'll use as we construct a sample, generic bastion host using HP-UX 11.00:

  1. Install HP-UX
  2. Install Additional Products
  3. Install Support Plus Bundle
  4. Install Security Patches
  5. First Steps
  6. Disable Network Services
  7. Disable Other Daemons
  8. Examine Set-id Programs
  9. Examine File Permissions
  10. Security Network Tuning
  11. Install Software and Test Configuration
  12. Create System Recovery Tape
Keep in mind that this is a sample starting configuration, and you will need to make changes specific to your planned use of the system. If you're installing a future HP-UX version like 11.10, some things may be different. You may also choose to reorder things slightly for various reasons. Every bastion host that I have configured has been different. Document your configuration steps as you perform them--you may discover later that a change that was made causes unforseen problems. And it may take several install iterations to get everything working correctly.

1. Install HP-UX

It takes at most one hour to install a minimal HP-UX configuration from CD-ROM. The security benefits of starting with a clean operating system install, and knowing exactly what you have, far exceed this minor cost in your time. Even if your host is new and has been shipped from the factory with HP-UX preinstalled, you should reinstall from scratch.

During the initial installation, configuration and testing, make sure that your system is not connected to any untrusted networks. You may want to only connect the system to a network after you have completed your configuration steps. In this example I used a completely private network (e.g., hub or cross-cable) connected only to the LAN console.

Note the test system used is an L2000, which will only run 64-bit HP-UX; we are also using the 9911 install media (11.ACE).

To perform the installation we boot from the install CD and perform the following steps:

  1. Select "Install HP-UX"
  2. In the "User Interface and Media Options" screen select:
    1. Media only installation
    2. Advanced Installation
  3. In the "Basic" screen select Environments "64-Bit Minimal HP-UX (English Only)"
  4. In the "Software" screen:
    1. Select "Change Depot Location"
    2. Change "Interactive swinstall" to "Yes"
    3. Select "Modify"
  5. Change other configuration settings as appropriate for your system
  6. Select "Go!"
  7. In the "SD Install" screen:
    1. Change the Software View to Products:
      View->Change Software View->Start with Products
    2. Mark MailUtilities.Runtime and MailUtilities.Manuals for Install
    3. Unmark NFS.Runtime.NIS-CLIENT for Install (this will also unmark KEY-CORE and NIS-CORE)
    4. Unmark NFS.Runtime.NFS-CLIENT for Install
    5. Mark NFS.Runtime.NFS-64SLIB for Install
    6. Unmark Networking.MinimumRuntime.PPP-RUN for Install
    7. Select OS-Core.Manuals for Install
    8. Select SOE for Install
    9. Select SecurityMon for Install
    10. Select Streams.Runtime.STREAMS-64SLIB for Install
    11. Select SystemAdmin.Runtime for Install
    12. Select TextEditors.Runtime and TextEditors.Manuals for Install
    13. Perform installation analysis:
      Actions->Install (analysis)
We choose a minimal HP-UX system. This will not install the X window system and many other products that we don't need or want. We remove as much of the NFS product as possible because it has a number of security problems and we will not be using it. We also remove the PPP-RUN fileset because we are not using PPP. For system management purposes we install SAM, the core OS man pages, mailers and text editors. We will be using the commercial security feature of HP-UX so we need to select the SecurityMon and SOE products. Finally, since we are installing on 64-bit hardware, we select the 64-bit libraries for NFS and STREAMS which are required for various applications.

We would like to remove other products such as SNMP (OVSNMPAgent) but a number of other products are dependent upon it (which seems questionable). We will disable SNMP and other products that are difficult or impossible to remove.

This yields a relatively lean configuration (much of the space in /var/ is for saved patches which we can optionally remove later) as shown by the following output of bdf, ps -ef and netstat -anf inet (but we still have work to do):

# uname -a
HP-UX bastion B.11.00 A 9000/800 137901517 two-user license

# bdf
Filesystem          kbytes    used   avail %used Mounted on
/dev/vg00/lvol3     143360   18699  116899   14% /
/dev/vg00/lvol1      83733   15965   59394   21% /stand
/dev/vg00/lvol8     512000  123680  364879   25% /var
/dev/vg00/lvol7     512000  164352  325949   34% /usr
/dev/vg00/lvol4      65536    1122   60394    2% /tmp
/dev/vg00/lvol6     262144    3513  242523    1% /opt
/dev/vg00/lvol5      20480    1109   18168    6% /home

# ps -ef
     UID   PID  PPID  C    STIME TTY       TIME COMMAND
    root     0     0  0 14:21:25 ?         0:10 swapper
    root     1     0  0 14:21:25 ?         0:00 init
    root     2     0  0 14:21:25 ?         0:00 vhand
    root     3     0  0 14:21:25 ?         0:00 statdaemon
    root     4     0  0 14:21:25 ?         0:00 unhashdaemon
    root     8     0  0 14:21:25 ?         0:00 supsched
    root     9     0  0 14:21:25 ?         0:00 strmem
    root    10     0  0 14:21:25 ?         0:00 strweld
    root    11     0  0 14:21:25 ?         0:00 strfreebd
    root    12     0  0 14:21:25 ?         0:00 ttisr
    root    18     0  0 14:21:25 ?         0:00 lvmkd
    root    19     0  0 14:21:25 ?         0:00 lvmkd
    root    20     0  0 14:21:25 ?         0:00 lvmkd
    root    21     0  0 14:21:25 ?         0:00 lvmkd
    root    22     0  0 14:21:25 ?         0:00 lvmkd
    root    23     0  0 14:21:25 ?         0:00 lvmkd
    root   826     1  0 14:25:12 console   0:00 -sh
    root   522     1  0 14:24:48 ?         0:00 /usr/sbin/ptydaemon
    root   870   866  1 14:30:26 console   0:00 ps -ef
    root    28     0  0 14:21:26 ?         0:00 vxfsd
    root   460     1  0 14:24:46 ?         0:00 /usr/sbin/syncer
    root   708     1  0 14:24:58 ?         0:00 /usr/sbin/snmpdm
    root   651     1  0 14:24:57 ?         0:00 /usr/sbin/rpcbind
    root   519     1  0 14:24:48 ?         0:00 /usr/sbin/syslogd -D
    root   535     1  0 14:24:49 ?         0:00 /usr/lbin/nktl_daemon 0 0 0 0 0 1 -2
    root   656     0  0 14:24:57 ?         0:00 nfskd
    root   545     1  0 14:24:52 ?         0:00 /usr/lbin/ntl_reader 0 1 1 1 1000 /var/adm/nettl /var/adm/co
    root   546   545  0 14:24:52 ?         0:00 /usr/sbin/netfmt -C -F -f /var/adm/nettl.LOG00 -c /var/adm/c
    root   746     1  0 14:25:09 ?         0:00 /usr/sbin/cron
    root   680     1  0 14:24:57 ?         0:00 /usr/sbin/inetd
    root   703     1  0 14:24:58 ?         0:00 sendmail: accepting connections on port 25
    root   866   826  0 14:28:53 console   0:00 ksh
    root   719     1  0 14:25:08 ?         0:00 /usr/sbin/hp_unixagt
    root   727     1  0 14:25:09 ?         0:06 /usr/sbin/mib2agt
    root   735     1  0 14:25:09 ?         0:00 /usr/sbin/trapdestagt
    root   743     1  0 14:25:09 ?         0:00 /usr/sbin/pwgrd
    root   749     1  0 14:25:09 ?         0:00 /usr/sbin/envd
    root   758     1  0 14:25:09 ?         0:00 /usr/sbin/swagentd -r

# netstat -anf inet
Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
tcp        0      0  *.7161                 *.*                     LISTEN
tcp        0      0  *.544                  *.*                     LISTEN
tcp        0      0  *.543                  *.*                     LISTEN
tcp        0      0  *.515                  *.*                     LISTEN
tcp        0      0  *.514                  *.*                     LISTEN
tcp        0      0  *.513                  *.*                     LISTEN
tcp        0      0  *.512                  *.*                     LISTEN
tcp        0      0  *.113                  *.*                     LISTEN
tcp        0      0  *.111                  *.*                     LISTEN
tcp        0      0  *.37                   *.*                     LISTEN
tcp        0      0  *.25                   *.*                     LISTEN
tcp        0      0  *.23                   *.*                     LISTEN
tcp        0      0  *.21                   *.*                     LISTEN
tcp        0      0  *.19                   *.*                     LISTEN
tcp        0      0  *.13                   *.*                     LISTEN
tcp        0      0  *.9                    *.*                     LISTEN
tcp        0      0  *.7                    *.*                     LISTEN
udp        0      0  *.2121                 *.*
udp        0      0  *.514                  *.*
udp        0      0  *.111                  *.*
udp        0      0  *.*                    *.*
udp        0      0  *.49152                *.*
udp        0      0  *.518                  *.*
udp        0      0  *.13                   *.*
udp        0      0  *.7                    *.*
udp        0      0  *.9                    *.*
udp        0      0  *.19                   *.*
udp        0      0  *.161                  *.*
udp        0      0  *.*                    *.*
udp        0      0  *.*                    *.*
udp        0      0  *.*                    *.*

2. Install Additional Products

At this point, you should install any additional HP products that are required on the bastion host, for example network drivers for add-on LAN cards, or other products you plan to use like LVM Mirror. You will want to install a portion of the HP Ignite product to obtain the software (make_recovery command) required to build a bootable backup tape of the root volume group, which we will create at the end of the configuration process.

For our sample configuration, we are using the 4-Port 100BT PCI card, so we need to install the driver for that card, and we will also install the required filesets in Ignite-UX for make_recovery functionality.

Using the December 1999 Applications CD we install the following product and filesets:

  1. 100BASE-T
  2. Ignite-UX.BOOT-KERNEL
  3. Ignite-UX.FILE-SRV-11-00
  4. Ignite-UX.MGMT-TOOLS
  5. Ignite-UX.RECOVERY

3. Install Support Plus Bundle

Next we install all General Release (GR) patches from the latest HP-UX 11.0 Support Plus CD, which in the example is from December 1999. The install CD contained a recent set of patches from around when the media was produced, which was November 1999, so we don't expect to have many patches that are selected. Mount the Support Plus CD and use swinstall to install the GR bundle XSWGR1100.

4. Install Security Patches

We next perform a security patch review, to determine if any security patches should be installed. HP-UX patches are available via anonymous FTP [3]. An "HP-UX Patch Security Matrix" [4] is also available, which contains a list of current security patches for each HP-UX platform and operating system version combination (e.g., s800 11.00). The matrix is updated nightly. There is also a list of the MD5 hash codes [5] for each patch which can be used to verify that patches you intend to install have not been tampered with (though it would be nice if this file was in turn PGP signed).

For our sample s800, 11.00 host, at the time of this writing, the current security patches are:

s800 11.00:PHCO_19945 s700_800 11.00 bdf(1M) patch to skip autofs file systems
           PHCO_20078 s700_800 11.0 Software Distributor (SD-UX) Cumulative Patch
           PHCO_20765 s700_800 11.00 libc cumulative patch
           PHKL_20315 s700_800 11.00 Cumulative LOFS patch
           PHNE_16295 s700_800 11.00 vacation patch.
           PHNE_17028 s700_800 11.00 r-commands cumulative mega-patch
           PHNE_17190 s700_800 11.00 sendmail(1m) 8.8.6 patch
           PHNE_17949 s700_800 11.00 Domain Management (DESMS B.01.12)
           PHNE_18017 s700_800 11.00 Domain Management (DESMS-NS B.01.11)
           PHNE_18377 s700_800 11.00 ftpd(1M) and ftp(1) patch
           PHNE_19620 s700_800 11.0 ONC cumulative patch
           PHNE_20619 s700_800 11.00 Bind 4.9.7 components
           PHNE_20735 s700_800 11.00 cumulative ARPA Transport patch
           PHSS_16649 s700_800 11.00 Receiver Services October 1998 Patch
           PHSS_17310 s700_800 11.00 OV OB2.55 patch - WinNT packet
           PHSS_17483 s700_800 11.00 MC/LockManager A.11.05 (English) Patch
           PHSS_17484 s700_800 11.00 MC/LockManager A.11.05 (Japanese) Patch
           PHSS_17496 s700_800 11.00 Predictive C.11.0[0,a-m] cumulative patch
           PHSS_17581 s700_800 11.00 MC ServiceGuard 11.05 Cumulative Patch
           PHSS_20385 s700_800 11.00 OV OB2.55 patch - DA packet
           PHSS_20544 s700_800 11.00 OV EMANATE14.2 Agent Consolidated Patch
           PHSS_20716 s700_800 11.00 CDE Runtime DEC99 Periodic Patch
Each patch for a product currently installed on the system should be analyzed to determine if it needs to be installed. First you should check and see if it's already installed from either the install media or the patch bundle. If not, you can look at the the patch .text file for details about the patch, including dependencies, filesets effected, and files patched. You can determine filesets installed on the system by executing swlist -l fileset.

Just because a patch exists doesn't mean that you need to install it, though it is safest to do so. Some patches may fix buffer overrun defects or other attack channels in set-uid root commands or root processes. If you plan to remove the set-uid bits you may choose not to install them. You may also not have a program configured (for example, rlogind listening on the network), but sometimes it can be difficult to determine if a defect is remotely or locally exploitable. If you're not sure whether a particular patch needs to be installed, it's best to just install it.

You should also examine the security bulletins themselves [6], because not all security bulletins result in a patch, for example there is a security bulletin regarding the default PMTU strategy that recommends its default be changed using ndd (HPSBUX0001-110) and also a serious issue with blank password fields when using Ignite-UX and trusted systems (HPSBUX0002-111). We will address the issue with the PMTU setting below when we set network security tunables, and the Ignite-UX issue concerns make_sys_image, which we will not be using.

5. First Steps

There are a few, miscellaneous configuration and cleanup steps we can perform immediately after the operating system install and patch steps.

  1. Optionally remove saved patches.

    By default during patch installation, rollback copies of all patch files modified are saved in /var/adm/sw/save/. You may wish to remove these files and claim the disk space by marking the patches "committed". However, if you do this, there will be no way to uninstall the patch with swremove. I tend to remove saved patches following a fresh install. To do this perform the following:

    # swmodify -x patch_commit=true '*.*'
    
  2. Convert to a trusted system.

    # /usr/lbin/tsconvert
    Creating secure password database...
    Directories created.
    Making default files. 
    System default file created...
    Terminal default file created...
    Device assignment file created...
    Moving passwords...
    secure password database installed.
    Converting at and crontab jobs...
    At and crontab files converted.
    # passwd root
    
    Passwords on existing accounts will expire as a result of the conversion, which is why we change the root password.

    You may also consider enabling auditing.

  3. Tighten global privileges.

    HP-UX has a feature known as privilege groups, which is mechanism to assign a privilege to a group (see privgrp(4)). By default the CHOWN privilege is a global privilege and applies to all groups:

    $ getprivgrp
    global privileges: CHOWN
    
    Non-privileged users really don't need to be able to chown files to other users; in Linux for example, only the super-user may change the owner of a file. /sbin/init.d/set_prvgrp is executed by default at system startup and executes the command /usr/sbin/setprivgrp -f /etc/privgroup if /etc/privgroup exists. We can create a configuration file that will delete all privileges for all groups (see setprivgrp(1m)):

    # getprivgrp
    global privileges: CHOWN
    # echo -n >/etc/privgroup
    # chmod 400 /etc/privgroup
    # /sbin/init.d/set_prvgrp start
    # getprivgrp
    global privileges:
    
  4. Fix PAM CDE problems.

    SAM will perform some correctness checks on /etc/pam.conf that involve trying to find a command using several different paths for each service_name. We did not install CDE and yet our pam.conf file contains dtlogin and dtaction entries for each of the PAM module types; for example:

    dtlogin  auth required  /usr/lib/security/libpam_unix.1
    dtaction auth required  /usr/lib/security/libpam_unix.1
    
    We can safely remove these, which will permit us to access the authenticated commands functionality in SAM:

    # cp /etc/pam.conf /etc/pam.conf.SAVE
    # grep -Ev '^(dtlogin|dtaction)' /etc/pam.conf.SAVE >/etc/pam.conf
    
  5. Fix hparray startup weirdness.

    For some reason there are some startup symlinks pointing to array startup scripts that are contained in filesets that we do not have and do not need (OS-Core.C2400-UTIL and OS-Core.ARRAY-MGMT) so we remove them:

    # for f in /sbin/rc*.d/*; do [ ! -f $f ] && echo $f; done
    /sbin/rc1.d/K290hparamgr
    /sbin/rc1.d/K290hparray
    /sbin/rc2.d/S710hparamgr
    /sbin/rc2.d/S710hparray
    # rm /sbin/rc1.d/K290hparamgr
    # rm /sbin/rc1.d/K290hparray
    # rm /sbin/rc2.d/S710hparamgr
    # rm /sbin/rc2.d/S710hparray
    
  6. Set default umask.

    One side-effect of converting to a trusted system, is the default umask of 0 is changed to 07077, so nothing needs to be performed to tighten up the umask.

  7. Restrict root login to the console if desired.

    # echo console > /etc/securetty
    # chmod 400 /etc/securetty
    
  8. Enable inetd logging if inetd will remain enabled.

    Add the -l (minus ell) argument to the INETD_ARGS environment variable in /etc/rc.config.d/netdaemons:

    export INETD_ARGS=-l
    
  9. Remove unneeded pseudo-accounts.

    First we examine some groups that might be removed, then users; our basic strategy is if there are no processes that are run with a given user or group, and there are no files owned by a user or group, we remove them:

    # find / -group lp -o -group nuucp daemon -exec ls -ld {} \;
    # groupdel lp
    # groupdel nuucp
    # groupdel daemon
    # find / -user uucp -o -user lp -o -user nuucp -o -user hpdb \
    > -o -user www -o -user daemon -exec ls -ld {} \;
    # userdel uucp
    # userdel lp
    # userdel nuucp
    # userdel hpdb
    # userdel www
    # userdel daemon
    
    For the remaining pseudo-accounts (bin, sys and adm), you should change the login shell to some invalid path, for example /, or consider using the noshell program from the Titan package [7].

    # pwget -n bin
    bin:*:2:2:NO LOGIN:/usr/bin:/
    
  10. Configure nsswitch.conf(4) policy.

    If you are going to configure the DNS resolver you can do it at this point. Many bastion hosts, including firewall gateways, do not have DNS configured at all. For these hosts, you can set the nsswitch.conf(4) to search local files only:

    # cp /etc/nsswitch.files /etc/nsswitch.conf
    # chmod 444 /etc/nsswitch.conf
    
  11. Change root home directory to /root.

    We change root's home directory from the default of / to /root. Our motivation is to give the root account a private home directory to lessen the possibility of files being placed unintentionally in /, and it also permits us to put a restrictive mode on the directory. Edit /etc/passwd and change root's entry to:

    root:*:0:3::/root:/sbin/sh
    
    Then build the directory and update the TCB:

    # mkdir /root
    # chmod 700 /root
    # mv /.profile /root
    # pwconv
    Updating the tcb to match /etc/passwd, if needed.
    

6. Disable Network Services

Disable inetd Services

We should be able to identify each TCP and UDP service emitted by netstat -af inet. Those that are not needed or cannot be secured should be disabled. Examples of such services include the UDP and TCP small servers, like echo, chargen, daytime, time and discard; the Berkeley r* services, talk, etc. Some bastion hosts have an entirely empty inetd.conf. We can start by removing all services from inetd.conf, restarting it, then examining the netstat output. If you stick with a bare inetd.conf, you can choose to not run inetd at all. You can disable inetd startup and shutdown by removing the corresponding symbolic links from the rc directories:

# rm /sbin/rc2.d/S500inetd
# rm /sbin/rc1.d/K500inetd
For the remaining services, consider using inetd.sec(4), which permits IP address based authentication of remote systems.

With all services removed from inetd.conf, netstat yields:

# netstat -af inet
Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
tcp        0      0  *.7161                 *.*                     LISTEN
tcp        0      0  *.portmap              *.*                     LISTEN
tcp        0      0  *.smtp                 *.*                     LISTEN
udp        0      0  *.2121                 *.*
udp        0      0  *.syslog               *.*
udp        0      0  *.portmap              *.*
udp        0      0  *.*                    *.*
udp        0      0  *.49152                *.*
udp        0      0  *.*                    *.*
udp        0      0  *.snmp                 *.*
udp        0      0  *.*                    *.*
udp        0      0  *.*                    *.*
This is much better, though we still need to determine what the remaining services are. We see that servers are listening on the UDP SNMP, portmap and syslog ports, and the SMTP and TCP portmap ports. However, 2121/udp, 2121/tcp, 7161/tcp and 49152/udp were not found in /etc/services, so netstat is unable to print the service name. There are also some wildcard (*.*) local UDP listeners that are a mystery.

An extremely useful tool for identifying network services is lsof (LiSt Open Files) [8]. lsof -i shows us the processes that are listening on the remaining ports:

# lsof -i
COMMAND   PID USER   FD   TYPE      DEVICE SIZE/OFF NODE NAME
syslogd   261 root    5u  inet 0x10191e868      0t0  UDP *:syslog (Idle)
rpcbind   345 root    4u  inet     72,0x73      0t0  UDP *:portmap (Idle)
rpcbind   345 root    6u  inet     72,0x73      0t0  UDP *:49158 (Idle)
rpcbind   345 root    7u  inet     72,0x72      0t0  TCP *:portmap (LISTEN)
sendmail: 397 root    5u  inet 0x10222b668      0t0  TCP *:smtp (LISTEN)
snmpdm    402 root    3u  inet 0x10221a268      0t0  TCP *:7161 (LISTEN)
snmpdm    402 root    5u  inet 0x10222a268      0t0  UDP *:snmp (Idle)
snmpdm    402 root    6u  inet 0x10221f868      0t0  UDP *:* (Unbound)
mib2agt   421 root    0u  inet 0x10223e868      0t0  UDP *:* (Unbound)
swagentd  453 root    6u  inet 0x1019d3268      0t0  UDP *:2121 (Idle)
We see that rpcbind is listening on 49158/udp (it's unclear whether this is a fixed or ephemeral port assignment) and snmpdm is listening on 7161/tcp. Also, we see that snmpdm and mib2agt are the source of the mysterious unbound wildcard ports.

Disable Other Services

With this information, we can proceed with the following steps.

  1. Prevent syslogd from listening on the network.

    PHCO_21023 can be installed which adds a -N option to syslogd to prevent it from listening on the network for remote log messages. After installing this patch, edit /sbin/init.d/syslogd and modify the line that starts syslogd to be /usr/sbin/syslogd -DN.

  2. Disable SNMP daemons.

    Edit SNMP startup configuration files:

    1. /etc/rc.config.d/SnmpHpunix
      Set SNMP_HPUNIX_START to 0: SNMP_HPUNIX_START=0
    2. /etc/rc.config.d/SnmpMaster
      Set SNMP_MASTER_START to 0: SNMP_MASTER_START=0
    3. /etc/rc.config.d/SnmpMib2
      Set SNMP_MIB2_START to 0: SNMP_MIB2_START=0
    4. /etc/rc.config.d/SnmpTrpDst
      Set SNMP_TRAPDEST_START to 0: SNMP_TRAPDEST_START=0

  3. Disable swagentd (SD-UX) daemon.

    This is complicated. The swagentd script is run twice in the bootup start sequence, and performs different tasks based upon its program name argument. For example, if run as S100swagentd it will remove the files listed in /var/adm/sw/cleanupfile. Also, for the swconfig script to work properly, swagentd must be running. Our solution is to create a new script, that will be configured to run immediately after S120swconfig to kill the swagentd daemon in a paranoid fashion, and remove the other start and kill rc links.

    The key portion of the kill script, swagentdk [9], follows:

    start)
            /usr/sbin/swagentd -k
            sleep 1
            findproc swagentd
            if [ "$pid" != "" ]; then
                    kill $pid
                    sleep 5
                    findproc swagentd
                    if [ "$pid" != "" ]; then
                            kill -9 $pid
                            sleep 5
                            findproc swagentd
                            if [ "$pid" != "" ]; then
                                    echo "UNABLE TO KILL SWAGENTD PROCESS!!!"
                                    rval=3  # REBOOT!!!
                            fi
                    else
                            rval=0
                    fi
            else
                    rval=0
            fi
            ;;
    
    We try to kill the daemon 3 times, with increasing levels of force. If we can't stop the daemon using kill -9, we set rval=3, which will cause a reboot (this drastic step may exceed your specific security and paranoia requirements).

    To configure, perform the following:

    # cp /tmp/swagentdk /sbin/init.d
    # chmod 555 /sbin/init.d/swagentdk
    # ln -s /sbin/init.d/swagentdk /sbin/rc2.d/S121swagentdk
    # rm /sbin/rc2.d/S870swagentd
    # rm /sbin/rc1.d/K900swagentd
    
  4. Disable sendmail daemon.

    Set the SENDMAIL_SERVER environment variable to 0 in /etc/rc.config.d/mailservs:

    export SENDMAIL_SERVER=0
    
  5. Disable rpcbind daemon.

    We don't plan to run any RPC services on the bastion host and need to disable the startup of rpcbind (this is the portmap replacement on HP-UX 11.0). After some grepping in /etc/rc.config.d we find that rpcbind is started from the nfs.core script, so we disable it in the rc startup directories. We also move the rpcbind program to a new name as an additional safety measure (though a patch install could reinstall it so it's important to reexamine your configuration after patches are installed on the bastion host):

    # rm /sbin/rc1.d/K600nfs.core
    # rm /sbin/rc2.d/S400nfs.core
    # mv /usr/sbin/rpcbind /usr/sbin/rpcbind.DISABLE
    
    This also avoids the startup of the nfskd process, which we saw in previous ps output.

After a reboot to verify the modifications made to the startup scripts, we can check the netstat and lsof output and verify that no network services remain enabled. We can also check the ps output again to verify that the disabled daemons were not launched:

# netstat -af inet
Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
udp        0      0  *.*
# lsof -i
# ps -ef
     UID   PID  PPID  C    STIME TTY       TIME COMMAND
    root     0     0  0 15:59:18 ?         0:10 swapper
    root     1     0  0 15:59:19 ?         0:00 init
    root     2     0  0 15:59:18 ?         0:00 vhand
    root     3     0  0 15:59:18 ?         0:00 statdaemon
    root     4     0  0 15:59:18 ?         0:00 unhashdaemon
    root     8     0  0 15:59:18 ?         0:00 supsched
    root     9     0  0 15:59:18 ?         0:00 strmem
    root    10     0  0 15:59:18 ?         0:00 strweld
    root    11     0  0 15:59:18 ?         0:00 strfreebd
    root    12     0  0 15:59:18 ?         0:00 ttisr
    root    18     0  0 15:59:19 ?         0:00 lvmkd
    root    19     0  0 15:59:19 ?         0:00 lvmkd
    root    20     0  0 15:59:19 ?         0:00 lvmkd
    root    21     0  0 15:59:19 ?         0:00 lvmkd
    root    22     0  0 15:59:19 ?         0:00 lvmkd
    root    23     0  0 15:59:19 ?         0:00 lvmkd
    root   367     1  0 15:59:48 console   0:00 -sh
    root   206     1  0 15:59:38 ?         0:00 /usr/sbin/syncer
    root   324     1  0 15:59:47 ?         0:00 /usr/sbin/inetd -l
    root    28     0  0 15:59:20 ?         0:00 vxfsd
    root   237     1  0 15:59:39 ?         0:00 /usr/sbin/ptydaemon
    root   380   367  0 16:00:03 console   0:00 ksh
    root   410   380  1 16:04:05 console   0:00 ps -ef
    root   250     1  0 15:59:40 ?         0:00 /usr/lbin/nktl_daemon 0 0 0 0 0 1 -2
    root   356     1  0 15:59:47 ?         0:00 /usr/sbin/cron
    root   260     1  0 15:59:42 ?         0:00 /usr/lbin/ntl_reader 0 1 1 1 1000 /var/adm/nettl /var/adm/co
    root   261   260  0 15:59:42 ?         0:00 /usr/sbin/netfmt -C -F -f /var/adm/nettl.LOG00 -c /var/adm/c
    root   352     1  0 15:59:47 ?         0:00 /usr/sbin/pwgrd
    root   359     1  0 15:59:47 ?         0:00 /usr/sbin/envd
    root   400     1  0 16:02:04 ?         0:00 /usr/sbin/syslogd -DN
For some unknown reason, netstat shows a wildcard UDP listener, but lsof is silent on this. This is a concern, and I have notified the HP-UX networking lab about this, and they are investigating.

7. Disable Other Daemons

We can now examine the current process listing and determine if there are other daemons that can be disabled. Our approach is: if we aren't using it, disable it. Many of the processes remaining are system processes. System processes can be identified by examining the flags column in a long process listing (ps -el); flags is an additive octal bit-field, like the Unix mode bits on files (see ps(1) for a listing of the process flag bits). The processes that have the 2 flag bit set (e.g. 1003, 01000 + 2 + 1) are system processes and can probably be ignored safely (the 01000 bit is explained below):

# ps -el
  F S        UID   PID  PPID  C PRI NI             ADDR   SZ            WCHAN TTY       TIME COMD
1003 S          0     0     0  0 128 20           6a4f58    0                - ?         0:10 swapper
141 S          0     1     0  0 168 20        101d3e600  100 400003ffffff0000 ?         0:00 init
1003 S          0     2     0  0 128 20        101b25f00    0           747e90 ?         0:00 vhand
1003 S          0     3     0  0 128 20        101b36200    0           5f2060 ?         0:00 statdaemon
1003 S          0     4     0  0 128 20        101b36500    0           6ec250 ?         0:00 unhashdaemon
1003 S          0     8     0  0 100 20        101b25300    0           72fed8 ?         0:00 supsched
1003 S          0     9     0  0 100 20        101b25600    0           6a3698 ?         0:00 strmem
1003 S          0    10     0  0 100 20        101b25900    0           6f2988 ?         0:00 strweld
1003 S          0    11     0  0 100 20        101b25c00    0           6cc2d0 ?         0:00 strfreebd
1003 S          0    12     0  0 -32 20        101b36800    0           6a0c68 ?         0:00 ttisr
1003 S          0    18     0  0 147 20        101b4c000    0           6a2fb0 ?         0:00 lvmkd
1003 S          0    19     0  0 147 20        101b4c300    0           6a2fb0 ?         0:00 lvmkd
1003 S          0    20     0  0 147 20        101b4c600    0           6a2fb0 ?         0:00 lvmkd
1003 S          0    21     0  0 147 20        101b4c900    0           6a2fb0 ?         0:00 lvmkd
1003 S          0    22     0  0 147 20        101b4cc00    0           6a2fb0 ?         0:00 lvmkd
1003 S          0    23     0  0 147 20        101b4cf00    0           6a2fb0 ?         0:00 lvmkd
  1 S          0   367     1  0 158 20        101e56100  106          31fff00 console   0:00 sh
  1 S          0   206     1  0 154 20        101df9b00    7           6a201c ?         0:00 syncer
  1 S          0   324     1  0 168 20        1019f0d00   24 400003ffffff0000 ?         0:00 inetd
1003 R          0    28     0  0 152 20        101b7a900    0                - ?         0:00 vxfsd
  1 S          0   237     1  0 155 20        1019cb600   20           701ef0 ?         0:00 ptydaemon
  1 S          0   380   367  0 158 20        101b60500   48          32011c0 console   0:00 ksh
  1 S          0   250     1  0 127 20        1019f6d00   15           623a74 ?         0:00 nktl_daemon
  1 S          0   356     1  0 154 20        101e56800   19        101b76d2e ?         0:00 cron
  1 S          0   260     1  0 127 20        1019a5200   18           6f2e8c ?         0:00 ntl_reader
  1 S          0   261   260  0 127 20        1019f8b00   29        1019f75c0 ?         0:00 netfmt
  1 S          0   352     1  0 154 20        101e3d500   46           746ca4 ?         0:00 pwgrd
  1 S          0   359     1  0 154 20        101e5db00   14        1019a652e ?         0:00 envd
  1 S          0   400     1  0 154 20        1019a7f00   21           746ca4 ?         0:00 syslogd
  1 R          0   413   380  0 157 20        1019a7400   25                - console   0:00 ps
Not all flag bits are documented in ps(1); undocumented flag bits include:

  • 040 - process' text locked in memory
  • 0100 - process' data locked in memory
  • 0200 - enables per-process syscall tracing
  • 0400 - process has one or more lazy swap regions
  • 01000 - process has 64-bit address space
This explains the 141 value seen for init: it has 0100 set because data is locked in memory, 040 because the text is locked in memory, and 1 because it's currently in core (0100 + 040 + 1 = 141), and the 1003 value for system processes like lvmkd (01000 + 2 + 1) which in this example, are 64-bit.

The list of non-system processes include:

  • init
  • syncer
  • inetd
  • ptydaemon
  • nktl_daemon, ntl_reader, netfmt
  • cron
  • pwgrd
  • envd
  • syslogd
By examining the man pages available for these daemons we determine that we need most of them. As mentioned earlier, you can disable inetd if you have no inetd-launched services. I suppose cron could be disabled if you do not plan to have any cron jobs, but that seems unlikely.

envd logs messages and can perform actions when over-temperature and chassis fan failure conditions are detected by the hardware. For example, in its default configuration it will execute /usr/sbin/reboot -qh when the temperature has exceeded the maximum operating limit of the hardware, in an attempt to preserve data integrity. I leave this daemon running, but you can disable its startup by modifying /etc/rc.config.d/envd.

nettl is the network tracing and logging subsystem, and in the system default configuration starts 3 daemons, ntl_reader, nktl_daemon and netfmt. These are easily disabled by editing /etc/rc.config.d/nettl, however you will lose potentially valuable log data, such as link down messages:

Apr  1 12:47:04 bastion vmunix: btlan: NOTE: MII Link Status Not OK - Check Cable Connection to Hub/Switch at 1/12/0/0/4/0....
Also, by default console logging is enabled. I find little value in log messages being written to a console that is rarely looked at or may in fact be non-existent. We can disable console logging which causes the console filter formatter daemon, netfmt to not start:

# nettlconf -L -console 0
# nettl -stop            
# nettl -start           
Initializing Network Tracing and Logging...
Done.
The nettlconf command modifies the nettl configuration file, /etc/nettlgen.conf, so this change will persist across system starts.

pwgrd is a password and group caching daemon. Since we have a very small password and group file it is unnecessary. Also, a little detective work with lsof and tusc (Trace Unix System Calls) [10] shows us that it listens on a Unix domain socket for client requests, and we don't want to allow command channels like that to processes running as root, so we have additional incentive to disable it:

Set the PWGR environment variable to 0 in /etc/rc.config.d/pwgr:

PWGR=0
We also remove stale sockets which will prevent unnecessary libc socket creation and requests to a nonexistent pwgrd listener:

# rm /var/spool/pwgr/*	# really just need to remove status
# rm /var/spool/sockets/pwgr/*
ptydaemon is a mystery, since it does not have a man page. A little more detective work leads us to the belief that it may only be used by vtydaemon, which we are not using. We decide to kill it and see if we can still login to the system remotely (we temporarily enable telnetd to test this). This works fine, so we decide to permanently disable the startup of ptydaemon:

Set the PTYDAEMON_START environment variable to 0 in /etc/rc.config.d/ptydaemon:

PTYDAEMON_START=0
Cleanup old logfile:
# rm /var/adm/ptydaemonlog

    8. Examine Set-id Programs

    Many Unix systems, including HP-UX, ship with numerous programs that are set-uid or set-gid. Many of these programs are not used or are only used by the root user. Many of the vulnerabilities that are discovered in Unix utilities rely on the set-uid root bit to raise privilege. You can improve the security of your system by removing these programs or by removing the set-id bit. To obtain a list of all files with either the set-uid or set-gid bit set on the system you can execute:

    # find / \( -perm -4000 -o -perm -2000 \) -type f -exec ls -ld {} \;
    
    You'll probably see well over 100 or so files listed (in the sample configuration there are 145). You may notice that there are two sets of LVM commands (in /sbin/ and /usr/sbin/), each with greater than 25 links, which are set-uid root. Also, the SD commands are set-uid root. The following permission changes will greatly reduce the size of your set-id list:

    # chmod u-s /usr/sbin/swinstall
    # chmod u-s /usr/sbin/vgcreate
    # chmod u-s /sbin/vgcreate
    
    You will also notice that there are some shared libs that have the set-uid bit set; the reason for this is unknown, however it is safe to remove them. If you did not previously remove all saved patch files in /var/adm/sw/save/, you may be surprised to see that they have retained their set-id privilege. While this practice is questionable, they are protected from being executable by non-root users due to the 500 mode on the /var/adm/sw/save/ directory.

    Our strategy is to remove the set-id bits from all files, then selectively add it back to just a few programs that need to be run by non-root users.

    The following commands will remove the set-uid and set-gid bits from all files, then add it back to su and the archive linked version of the passwd command:

    # find / -perm -4000 -type f -exec chmod u-s {} \;
    # find / -perm -2000 -type f -exec chmod g-s {} \;
    # chmod u+s /usr/bin/su
    # chmod u+s /sbin/passwd
    
    The commands you choose to leave set-id depend on the specific usage and policies of your bastion host. Let's say that the bastion host is a firewall gateway, where a few administrators will login via a unique, personal login, then su to root to manage the gateway. Here, /usr/bin/su may be the only program on the system that needs to be set-uid.

    Additionally, a number of commands will function fine without privilege using default or commonly used options, including bdf, uptime and arp--however some functionality may be lost for non-root users. For example, you can no longer specify a filesystem argument for bdf:

    $ bdf /dev/vg00/lvol3
    bdf: /dev/vg00/lvol3: Permission denied
    

    9. Examine File Permissions

    A freshly installed HP-UX system will contain a number of files which are writable by other (the 002 bit is set in the mode bits). These files can be listed with the following:

    # find / -perm -002 ! -type l -exec ls -ld {} \;
    
    We don't display symbolic links with the write other bit set because the mode bits are not used for permission checking.

    One approach is to remove the write other bit from all files then selectively add it back to those files and directories where it is necessary. The following can be executed to remove the write other bit from all files with it set:

    # find / -perm -002 ! -type l -exec chmod o-w {} \;
    
    Now we open up the permissions of files that need to be writable by other users:

    # chmod 1777 /tmp /var/tmp /var/preserve
    # chmod 666 /dev/null
    
    Note that we also set the sticky bit (01000) in publicly writable directories like /tmp and /usr/tmp. This prevents unprivileged users from removing or renaming files in the directory that are not owned by them (see chmod(2)).

    10. Security Network Tuning

    HP-UX 11 introduces the ndd command to perform network tuning. ndd -h produces a list of help text for each supported and unsupported ndd tunable parameter that can be changed. After examining this list, we decide the following are candidates for changing on a bastion host:

    Network device Parameter Default value Suggested value Comment
    /dev/ip ip_forward_directed_broadcasts 1 0 Don't forward directed broadcasts
    /dev/ip ip_forward_src_routed 1 0 Don't forward packets with source route options
    /dev/ip ip_forwarding 2 0 Disable IP forwarding
    /dev/ip ip_ire_gw_probe 1 0 Disable dead gateway detection (currently no ndd help text; echo-requests interact badly with firewalls)
    /dev/ip ip_pmtu_strategy 2 1 Don't use echo-request PMTU strategy (can be used for amplification attacks and we don't want to send echo-requests anyway)
    /dev/ip ip_send_redirects 1 0 Don't send ICMP redirect messages (if we have no need to send redirects)
    /dev/ip ip_send_source_quench 1 0 Don't send ICMP source quench messages (deprecated)
    /dev/tcp tcp_conn_request_max 20 500 Increase TCP listen queue maximum (performance)
    /dev/tcp tcp_syn_rcvd_max 500 500 HP SYN flood defense
    /dev/ip ip_check_subnet_addr 1 0 Permit 0 in local network part (should be the default)
    /dev/ip ip_respond_to_address_mask_broadcast 0 0 Don't respond to ICMP address mask request broadcasts
    /dev/ip ip_respond_to_echo_broadcast 1 0 Don't respond to ICMP echo request broadcasts
    /dev/ip ip_respond_to_timestamp_broadcast 0 0 Don't respond to ICMP timestamp request broadcasts
    /dev/ip ip_respond_to_timestamp 0 0 Don't respond to ICMP timestamp requests

    Some of the default values match our preferred value, but we can choose to set them anyway, just in case the default should change in a future release. ndd supports a -c option which reads a list of tunables and values from the file /etc/rc.config.d/nddconf, and which is run automatically at boot time. However, there are some problems with the default setup. First, at the time of this writing, ndd -c is only able to handle 10 tunables in nddconf. Next, ndd -c is run at the end of the net script, which is after network interfaces have been configured. One issue with this is it is too late to set ip_check_subnet_addr if we are using subnet zero in the local part of a network. But more importantly, we want to set tunables before the network interfaces are configured (note: the ordering problem has been fixed in a recent transport patch, but the 10 tunable limit remains).

    A workaround is presented that uses a new startup script and configuration file:

    # cp /tmp/secconf /etc/rc.config.d
    # chmod 444 /etc/rc.config.d/secconf
    # cp /tmp/sectune /sbin/init.d
    # chmod 555 /sbin/init.d/sectune
    # ln -s /sbin/init.d/sectune /sbin/rc2.d/S009sectune
    
    We run the script immediately after net.init, which sets up the plumbing for the IP stack, then runs ndd -a which sets transport stack tunable parameters to their default value.

    sectune and a sample secconf are available for download [11].

    11. Install Software and Test Configuration

    At this point you can install, test and configure the application software that you will use on the bastion host, such as the BIND product, a web server, a firewall product etc. Security software, such as SSH (Secure Shell) and TCP wrappers can be installed at this point, as determined by the specific security requirements and use of the bastion host. Again, extreme caution should be exercised when installing new software on your bastion host. You should generally get the latest version of the product, that has been patched against all known security defects. You may want to install the product first on another system and determine if it can be secured. Think like an attacker, and ensure that the bastion host is able to protect itself with the product installed.

    12. Create System Recovery Tape

    Next we create a bootable System Recovery Tape of the root volume group; this tape can also be used to clone the system to other hardware that is supported with the same software configuration (for example I can clone from an L2000 to an N4000).

    The following can be executed online (very cool), though I gather you will want the system in a somewhat quiescent state:

    # /opt/ignite/bin/make_recovery -Ai 
          Option -A specified. Entire Core Volume Group/disk will be backed up.
    
    
    
          ***************************************
           HP-UX System Recovery
           Going to create the tape.
           System Recovery Tape successfully created.
    

    Conclusion

    With the simple methodology presented, a paranoid mindset, a little detective work and some persistence, it's relatively straightforward to construct a robust bastion host using HP-UX.

    References

    [1] Marcus J. Ranum, "Thinking About Firewalls", SANS 1993. An updated version, "Thinking About Firewalls V2.0: Beyond Perimeter Security", is available at http://www.clark.net/pub/mjr/pubs/think/index.htm

    [2] D. Brent Chapman and Elizabeth D. Zwicky, "Building Internet Firewalls", O'Reilly & Associates, September 1995.

    [3] HP-UX patches are available via anonymous FTP in North America at ftp://us-ffs.external.hp.com/hp-ux_patches/; and Europe at ftp://europe-ffs.external.hp.com/hp-ux_patches/.

    [4] HP-UX Patch Security Matrix, ftp://europe-ffs.external.hp.com/export/patches/hp-ux_patch_matrix.

    [5] HP-UX Patch Checksum Information, ftp://europe-ffs.external.hp.com/export/patches/hp-ux_patch_sums.

    [6] HP Security Bulletins are available at http://us-support.external.hp.com/ and http://europe-support.external.hp.com/. Select "Search Technical Knowledge Base" (unfortunately you need a login to access security bulletins, but you can register for one in a few minutes).

    [7] Titan host security tool, http://www.fish.com/titan/.

    [8] Vic Abell's lsof (LiSt Open Files), ftp://vic.cc.purdue.edu/pub/tools/unix/lsof/.

    [9] swagentdk script, http://people.hp.se/stevesk/swagentdk.

    [10] tusc (Trace Unix System Calls), syscall tracer for HP-UX, ftp://ftp.cup.hp.com/dist/networking/misc/tusc.shar.

    [11] Sample secconf and sectune scripts, http://people.hp.se/stevesk/secconf and http://people.hp.se/stevesk/sectune.

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