Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-97.114 -- SNI Security Advisory Vacation Vulnerability 3 September 1997 =========================================================================== Secure Networks Inc. has released the following advisory concerning a vulnerability in the vacation program. This vulnerability may allow remote users to obtain access to the account of any local user running the vacation program. The following security bulletin is provided as a service to AUSCERT's members. As AUSCERT did not write this document, AUSCERT has had no control over its content. As such, the decision to use any or all of this information is the responsibility of each user or organisation, and should be done so in accordance with site policies and procedures. Contact information for SNI is included in the Security Bulletin below. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/information/advisories.html If you believe that your system has been compromised, contact AUSCERT or your representative in FIRST (Forum of Incident Response and Security Teams). Internet Email: email@example.com 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. - ---------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- ##### ## ## ###### ## ### ## ## ##### ## # ## ## ## ## ### ## ##### . ## ## . ###### . Secure Networks Inc. Security Advisory September 1, 1997 Vacation Vulnerability This advisory addresses a vulnerability in the vacation program which allows individuals to execute commands remotely on vulnerable systems. Vacation is used by the recipient of email messages to notify the sender that they are not currently reading their mail. This is installed by placing a .forward file into your directory containing a line as follows: user, "|/usr/bin/vacation user" Problem Description ~~~~~~~~~~~~~~~~~~~ When vacation responds to an incoming message, it invokes the sendmail command, specifying the address of the sender on the command line. By specifying a sendmail command line option rather than a valid email address, it is possible to cause sendmail to be invoked with an alternate configuration file. This alternate configuration file can be previously sent to the system via a seperate email message, or via anonymous FTP. When parsed, this new sendmail configuration file can cause sendmail to execute arbitrary commands on the remote system. Technical Details ~~~~~~~~~~~~~~~~~ By specifying the originating address of an email message to consist of a path to an alternate configuration file (i.e. -C/var/mail/user), the vacation program will invoke sendmail, and use /var/mail/user as the configuration file. If the user's mailbox contains valid sendmail configuration options, sendmail will treat the user's mail spool as a sendmail configuration file. Sendmail can be induced execute arbitrary shell commands from its configuration file. Variations on this attack may be possible using sendmail options other than -C. Impact ~~~~~~ Remote individuals can obtain access to the account of any user running the vacation program. Vulnerable Systems ~~~~~~~~~~~~~~~~~~ The following assessments assume that an attacker can utilize the -C command line option of sendmail to specify an alternate configuration file and execute commands. Other methods of causing sendmail to execute commands via command line options may be present. Operating systems which ship with a vulnerable version of vacation are: AIX Version 4.2 is vulnerable. Version 4.1 is also vulnerable if public domain version of sendmail 8 has been installed. FreeBSD All versions prior to August 28, 1997. NetBSD All versions prior to NetBSD-current 19970828 are vulnerable. OpenBSD All versions prior to July 29, 1997 Solaris All versions of Solaris are vulnerable ONLY if a public domain version of sendmail has been installed, other than Solaris sendmail. Linux The two versions of vacation on the sunsite.unc.edu Linux archive are both vulnerable as of August 5, 1997. Linux distributions we have verified do not ship with the vacation program. HP-UX HP-UX is vulnerable ONLY if a public domain version of sendmail, other than HP-UX sendmail has been installed. BSD/OS (BSDI) is NOT vulnerable to this problem. Silicon Graphics IRIX does NOT APPEAR to be vulnerable to this problem. Fix Information ~~~~~~~~~~~~~~~ IBM AIX Only the version of vacation shipped with AIX 4.2 is vulnerable. The following APAR will be available soon: Abstract: "SECURITY: /usr/bin/vacation vulnerability" AIX 4.1: IX70228 AIX 4.2: IX70233 Until these fixes are applied, the vacation program should be disabled with the following command (as root): # chmod -x /usr/bin/vacation If disabling vacation is not desirable, there is a temporary fix available via anonymous ftp: ftp://testcase.software.ibm.com/aix/fromibm/vacation.security.tar.Z IBM and AIX are registered trademarks of International Business Machines Corporation. HP-UX The version of vacation shipped with HP-UX is vulnerable. This vulnerability is exploitable by remote users only if the system administrator has installed a version of sendmail version 8, other than HP sendmail. HP will be providing a fix in the near future. Solaris The version of vacation shipped with Solaris is vulnerable if a public domain version of sendmail, other than Solaris sendmail, has been installed on the system. Sun Microsystems will be issuing a solution to this problem in the near future. As a short term workaround, the vacation program be disabled by changing the permissions as follows: # chmod -x /bin/vacation OpenBSD 2.1 This problem is present in OpenBSD-current prior to August 29, 1997. Update your vacation sources to the version in -current using anoncvs, or apply the fix provided below. Then recompile the vacation program. See http://www.openbsd.org for information about anoncvs. FreeBSD FreeBSD has corrected this problem in 2.1-stable, 2.2-stable and 3.0-current as of August 28, 1997. The source change described in this advisory corrects the problem. This problem will be fixed in the upcoming 2.2.5-RELEASE and 3.0-RELEASE versions of FreeBSD. NetBSD This problem is present in NetBSD-current prior to 19970828 and is fixed in later releases. Upgrade to a version of NetBSD-current newer than 19970828 or apply the fix provided below. Other Obtain a patched version of vacation at the following location: ftp://ftp.secnet.com/pub/patches/vacation.tar.Z To extract the archive when it is in the current directory, issue the commands: % uncompress vacation.tar % tar -xvf vacation.tar Then follow the installation instructions in the README file included in the archive. Please note that this version of vacation is taken from BSD sources, and may require modification to work on other platforms. The following patch, suggested independently by Eric Allman and Keith Bostic, solves the problem. Note that SNI has *not* verified that sendmail versions other than sendmail version 8 properly emulate getopt() in their interpretation of the option "--". If you are applying this patch to an operating system which ships with a modified or older version of sendmail, you should verify that the sendmail command-line options which are *not* done using getopt() do not get parsed if they are preceeded by a '--' option. The following line: execl(_PATH_SENDMAIL, "sendmail", "-f", myname, from, NULL); should be substituted with: execl(_PATH_SENDMAIL, "sendmail", "-f", myname, "--", from, NULL); in vacation.c Additional Information ~~~~~~~~~~~~~~~~~~~~~~ The provided generic fix was suggested by both Eric Allman <firstname.lastname@example.org> and Keith Bostic <email@example.com> This problem was discovered by David Sacerdote <firstname.lastname@example.org>, and verified by David Sacerdote <email@example.com> and Oliver Friedrichs <firstname.lastname@example.org>. You can subscribe to our security advisory mailing list by sending mail to email@example.com, containing the single line subscribe sni-advisories You can find Secure Networks papers at ftp://ftp.secnet.com/pub/papers or http://www.secnet.com/papers and past advisories at ftp://ftp.secnet.com/pub/advisories or http://www.secnet.com/advisories You can contact Secure Networks Inc. at <firstname.lastname@example.org> using the following PGP key: Type Bits/KeyID Date User ID pub 1024/9E55000D 1997/01/13 Secure Networks Inc. <email@example.com> Secure Networks <firstname.lastname@example.org> - - -----BEGIN PGP PUBLIC KEY BLOCK----- Version: 2.6.3ia mQCNAzLaFzIAAAEEAKsVzPR7Y6oFN5VPE/Rp6Sm82oE0y6Mkuof8QzERV6taihn5 uySb31UeNJ4l6Ud9alOPT/0YdeOO9on6eD1iU8qumFxzO3TLm8nTAdZehQSAQfoa rWmpwj7KpXN/3n+VyBWvhpBdKxe08SQN4ZjvV5HXy4YIrE5bTbgIhFKeVQANAAUR tCVTZWN1cmUgTmV0d29ya3MgSW5jLiA8c25pQHNlY25ldC5jb20+iQCVAwUQM1yd EB/bLKAOe7p9AQFptAQAiYpaZCpSmGgr05E698Z3t5r5BPAKUEtgvF53AvZUQLxz ZsYsVU5l5De0qKWJOQ/9LiDyWu1lvKhlTphbLy2RatWD4kO3oQL9v3TpSXm2WQhU uIzyZvj7S5ENodNnKn+gCDIvbou6OMot+7dRbWWgN2oabbru4CSlOxbG++yaTz+J AJUDBRAzTefbtOXez5VgyLkBAd0bA/43eGEgvPOFK+HHWCPpkSWCwtrtDU/dxOVz 9erHnT/CRxeojCI+50f71Qe+kvx9Q1odz2Jl/fLxhnPQdbPnpWblIbu4F8H+Syrj HTilDrl1DWa/nUNgK8sb27SMviELczP1a8gwA1eo5SUCG5TWLLTAzjWOgTxod2Ha OwseUHmqVIkAlQMFEDNOVsr/d6Iw8NVIbQEBxM0D/14XRfgSLwszgJcVbslMHm/B fF6tHoWYojzQle3opOuMYHNN8GsMZRkc1qQ8QuNA9Aj5+qDqEontGjV5IvhBu1fY FM77AhagskaFCZxwqV64Qrk328WDO89NGSd+RuovVNruDdn20TxNCEVuPTHjI0UA 8H+E6FW9jexg6RTHhPXYtCVTZWN1cmUgTmV0d29ya3MgPHNlY3VyaXR5QHNlY25l dC5jb20+iQCVAwUQMtqTKB/bLKAOe7p9AQFw5wQAgUwqJ+ZqfEy/lO1srU3nzxLA X0uHGHrMptRy/LFo8swD6G1TtWExUc3Yv/6g2/YK09b5WmplEJ+Q09maQIw+RU/s cIY+EsPauqIq4JTGh/Nm0Z4UDl2Y1x4GNtm0YqezxUPS0P0A3LHVLJ3Uo5og0G8O gPNrfbVz5ieT14OSCWCJAJUDBRAy2hd2/3eiMPDVSG0BAVNhBACfupfAcNhhnQaq aI03DOOiZSRjvql1xw4V+pPhM+IksdSK3YNUZVJJtANacgDhBT+jAPRaYbBWI3A5 ZMdcSNM8aTG0LWMLIOiOYEm6Lgd3idRBFN0Js08eyITl8mhZ33mDe4I0KQri9UiV ZcPYTbb9CWM6Hv2cMbt6S6kLnFziqIkAlQMFEDLaF0+4CIRSnlUADQEBCLoEAJwt UofDgvyZ4nCDx1KKAPkkXBRaPMWBp46xeTVcxaYiloZfwHfpk1h2mEJAxmAsvizl OtIppHl4isUxcGi/E2mLCLMvis22/IQP/9obPahPvgNaMLVtZljO1Nv3QFEkNciL FEUTNJHR1ko7ibCxkBs4cOpirFuvTMDvWnNaXAf8 =DchE - - -----END PGP PUBLIC KEY BLOCK----- Copyright Notice ~~~~~~~~~~~~~~~~ The contents of this advisory are Copyright (C) 1997 Secure Networks Inc, and may be distributed freely in unmodified form provided that no fee is charged for distribution, and that proper credit is given. - -----BEGIN PGP SIGNATURE----- Version: 2.6.3ia Charset: noconv iQCVAwUBNAu+J7gIhFKeVQANAQGylwP+Kb5azwj3O9gns7/7v8Qk2q4gE1bpaF2y KhyiRLyQpQUC0dTYpR3J3u2TmfhXnDfavYnkMeEWjvMHp0d/h6/KQ2Qk3VyYZbTL yQXSrlqSlP+lxXdfHaqwNOfLWP7DrZ7r8NwH/FOlosPtMgYsVOv+97SxSmkSubIm K5MiCxBZS/k= =KJTq - -----END PGP SIGNATURE----- - ---------------------------END INCLUDED TEXT-------------------- -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBNA/2eih9+71yA2DNAQF5HAQAmCzLgtBYkd3hJCbizx4RVsEKFdKo/cm+ cBI977z7NgzLQNHJNcLnU6XpX63h33BxYnG0mSHAxjwykdAZ7q4xh9OYK9qp/jYZ kP9I+HHY68Ht8krhx03UgjMBhS1gY3anRRhlKfE50uU9DAJfXe/p+VsX/ypDbC4M Q+j7ydIi9lk= =sAQy -----END PGP SIGNATURE-----