-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AA-97.26 AUSCERT Advisory HP-UX cue Vulnerability 4 September 1997 Last Revised: -- - --------------------------------------------------------------------------- AUSCERT has received information that a vulnerability exists in the HP-UX program cue(1). This vulnerability may allow local users to gain root privileges. Exploit information involving this vulnerability has been made publicly available. At this stage, AUSCERT is unaware of any official vendor patches. AUSCERT recommends that sites apply the workaround given in Section 3 until vendor patches are made available. This advisory will be updated as more information becomes available. - --------------------------------------------------------------------------- 1. Description The HP-UX cue(1) program is used to start the Character-Terminal User Environment (CUE) for users. cue is often started from cuegetty(1M) but may also be started from the command line or via a user's initialisation script (for example, .login). It has been discovered that cue creates files in an insecure manner. As this program is setuid root, it may be possible for local users to create or overwrite arbitrary files on the system. Exploit information involving this vulnerability has been made publicly available. cue is installed by default in /usr/bin/cue under HP-UX 9.x and 10.x on Series 800 machines. Although cue should only be installed on Series 800 machines, sites are encouraged to check for its presence on all machines running HP-UX and, if found, implement workarounds given in Section 3. 2. Impact Local users may be able to create or over-write arbitrary files on the system. This can be leveraged to gain root privileges. 3. Workarounds/Solution AUSCERT recommends that sites prevent the exploitation of the vulnerability in cue by immediately applying the workaround given in Section 3.1. If the functionality provided by CUE is required for a small set of trusted users, AUSCERT recommends that access to the cue program be restricted to this group as described in Section 3.2. Hewlett Packard has informed AUSCERT that they are aware of this problem and a resolution is in progress. AUSCERT recommends that official vendor patches be installed when they are made available. 3.1 Remove setuid and execute permissions Until official vendor patches are made available, sites should remove the setuid root and execute permissions from cue. To do this, the following command should be run as root: # chmod 400 /usr/bin/cue # ls -l /usr/bin/cue -r-------- 1 root bin 1564672 Jun 10 1996 /usr/bin/cue Note that this will remove the ability for any user to run this program. 3.2 Restrict access If the functionality provided by the cue program is required by a small set of trusted users, sites may wish to restrict the execution of cue to that group of users. For example, if the Unix group "trusted" exists and contains only those users allowed to use cue, the following commands will restrict its use: # chgrp trusted /usr/bin/cue # chmod 4750 /usr/bin/cue # ls -l /usr/bin/cue -rwsr-x--- 1 root trusted 1564672 Jun 10 1996 /usr/bin/cue Access to any account in the "trusted" group will allow vulnerable versions of cue to be exploited. 4. Additional measures 4.1 Check old patch directories During the installation of HP-UX patches, copies of files being replaced are saved in case the patches need to be uninstalled. The original versions of patched files are stored in the following locations: HP-UX 9.x: /system//orig/ HP-UX 10.x: /var/adm/sw/patch/PATCH_NAME>/ If patches for vulnerable programs have been previously installed, copies of the vulnerable programs may be available in the above locations. Sites should ensure the directories have permissions which restrict access to the patch areas. 4.2 Remove unnecessary setuid/setgid programs Most Unix systems ship with numerous programs which have setuid or setgid privileges. Often the functionality supplied by these privileged programs is not required by many sites. The large number of privileged programs that are shipped by default are to cater for all possible uses of the system. AUSCERT encourages sites to examine all the setuid/setgid programs and determine the necessity of each program. If a program does not absolutely require the setuid/setgid privileges to operate (for example, it is only run by the root user), the setuid/setgid privileges should be removed. Furthermore, if a program is not required at your site, then all execute permissions should be removed. A sample command to find all setuid/setgid programs is (run as root): # find / \( -perm -4000 -o -perm -2000 \) -type f -exec ls -l {} \; It is AUSCERT's experience that many vulnerabilities are being discovered in setuid/setgid programs which are not necessary for the correct operation of most systems. Sites can increase their security by removing unnecessary setuid/setgid programs. For example, the functionality provided by the cue program is not needed by most sites. If sites had previously disabled the cue program, they would not have been vulnerable to this latest exploit. - --------------------------------------------------------------------------- AUSCERT thanks Hewlett-Packard for their continued assistance and technical expertise essential for the production of this advisory. AUSCERT also thanks Information Technology Services of the University of Southern Queensland for their assistance. - --------------------------------------------------------------------------- The AUSCERT team have made every effort to ensure that the information contained in this document is accurate. However, the decision to use the information described is the responsibility of each user or organisation. The appropriateness of this document for an organisation or individual system should be considered before application in conjunction with local policies and procedures. AUSCERT takes no responsibility for the consequences of applying the contents of this document. If you believe that your system has been compromised, contact AUSCERT or your representative in FIRST (Forum of Incident Response and Security Teams). AUSCERT is located at The University of Queensland within the Prentice Centre. AUSCERT is a full member of the Forum of Incident Response and Security Teams (FIRST). AUSCERT maintains an anonymous FTP service which is found on: ftp://ftp.auscert.org.au/pub/. This archive contains past SERT and AUSCERT Advisories, and other computer security information. AUSCERT also maintains a World Wide Web service which is found on: http://www.auscert.org.au/. Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 4477 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AUSCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for emergencies. Postal: Australian Computer Emergency Response Team Prentice Centre Brisbane Qld. 4072. AUSTRALIA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Revision History ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBNA6MNCh9+71yA2DNAQFIRwQAhxwzyxz+ILt8ZOiur+Ln6l+14wWviBpF HSR9d+NPmo2Xcg1ga5d28e3MgGQm7zMLqHbREWDjCRk2SLdcQiUz9cP6gI2KLize XKfkfPW8uVxGyqClTluL/a6Zw5wQ+zh6qA3XeOzpRmmeFXUHu4/FOIj+mRbfninp dEGCVTk+EwE= =7z5/ -----END PGP SIGNATURE-----