-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= CERT* Advisory CA-96.08 Original issue date: April 18, 1996 Last revised: April 3, 1997 Minor changes: corrected a name in the acknowledgments; indicated that CERT is now a registered service mark A complete revision history is at the end of this file. Topic: Vulnerabilities in PCNFSD - ----------------------------------------------------------------------------- The CERT Coordination Center has received reports of two vulnerabilities in the pcnfsd program (pcnfsd is also known as rpc.pcnfsd); we have also received reports that these problems are being exploited. These vulnerabilities are present in some vendor-provided versions of pcnfsd and in some publicly available versions. These two vulnerabilities were reported by Avalon Security Research in reports entitled "pcnfsd." If you are using a vendor-supplied version of pcnfsd, please see the vendor information in Section III.A and Appendix A. Until you can install a patch from your vendor for these vulnerabilities, consider using the publicly available version described in Section III.B. If you already use or plan to switch to a public version, we urge you to use the version cited in Section III.B or install the patch described in Section III.C. This patch has already been incorporated into the pcnfsd version described in III.B. There are many different public domain versions of pcnfsd, and we have not analyzed the vulnerability of those versions. We have analyzed and fixed the problems noted in this advisory only in the version described in III.B. We will update this advisory as we receive additional information. Please check advisory files regularly for updates that relate to your site. - ----------------------------------------------------------------------------- I. Description The pcnfsd program (also called rpc.pcnfsd) is an authentication and printing program that runs on a UNIX server. There are many publicly available versions, and several vendors supply their own version. pcnfsd supports a printing model that uses NFS to transfer files from a client to the pcnfsd server. (Note: pcnfsd does *not* provide NFS services.) When a client wants to print a file, it requests the path to a spool directory from the server. The client then writes the necessary files for printing using NFS, and informs the pcnfsd server that the files are ready for printing. pcnfsd creates a subdirectory for each of its clients using the client's hostname, then returns this path name to the client. The returned path name must be exported via to its clients by the NFS server. The NFS server and the pcnfsd server may be two separate machines. The first vulnerability is that pcnfsd, which runs as root, creates the aforementioned directories with mkdir(2) and then changes their mode with chmod(2) to mode 777. If the target directory is replaced with a symbolic link pointing to a restricted file or directory, the mkdir(2) will fail but the chmod(2) will succeed. This means that the target of the symbolic link will be mode 777. Note that pcnfsd must run as root when servicing print requests so that it can assume the identity of the PC user when interacting with UNIX print commands. On some systems, pcnfsd may also have to run as root so it can read restricted files when carrying out authentication tasks. The second vulnerability is that pcnfsd calls the system(3) subroutine as root, and the string passed to system(3) can be influenced by the arguments given in the remote procedure call. Remote users can execute arbitrary commands on the machine where pcnfsd runs. II. Impact For the first vulnerability, local users can change the permissions on any file accessible to the local system that the root user can change. For the second vulnerability, remote users can execute arbitrary commands as root on the machine where pcnfsd runs. The impact is that directories can become world writable (mode 777). What this can lead to is bounded by the creativity of the intruder. For example, once the mode of /etc were changed to mode 777, one could then replace the password file, and then go on from there. Exploitation of these vulnerabilities is only part of a larger attack scenario. Once exploited, there are many pathologies that could follow. III. Solution If you are using pcnfsd from a vendor, consult the vendor list in Section A. If your vendor is not listed, we recommend that you contact your vendor directly. Until a vendor patch is available, we recommend that you obtain the publicly available version of pcnfsd as described in Section B. This version already has the patch described in Section C. If you are presently using a public version of pcnfsd, we recommend that you either change to the version listed in Section B or apply the patch described in Section C. (The version in Section B already contains this patch.) A. Obtain and install the appropriate patch according to the instructions included with the patch. Below is a list of the vendors who have reported to us as of the date of this advisory. More complete information, is provided in the appendix. We will update the appendix as we receive more information. If your vendor's name is not on this list, please contact the vendor directly. Vendor or Source Status ---------------- ------------ BSDI BSD/OS Vulnerable. Patch available. Hewlett Packard Vulnerable. Patch under development. IBM AIX 3.2 Vulnerable. Patches available. IBM AIX 4.1 Vulnerable. Patches available. NEXTSTEP Vulnerable. Will be fixed in version 4.0. SCO OpenServer 5 Vulnerable. Patch under development. SCO UnixWare 2.1 Vulnerable. Patch under development. SGI IRIX 5.3 Vulnerable. Patch under development. SGI IRIX 6.2 Not vulnerable. B. Until you are able to install the appropriate patch, we recommend that you obtain a version of pcnfsd from one of the following locations. This version already has the patch mentioned in Section III.C. ftp://ftp.cert.org/pub/tools/pcnfsd/pcnfsd.93.02.16-cert-dist.tar.Z ftp://ftp.cert.dfn.de/pub/tools/net/pcnfsd/pcnfsd.93.02.16-cert-dist.tar.Z MD5 (pcnfsd.93.02.16-cert-dist.tar.Z) = b7af99a07dfcf24b3da3446d073f8649 Build, install, and restart rpc.pcnfsd. Ensure that the mode of the top-level pcnfsd spool directory is 755. In this version of pcnfsd, the top level spool directory is /usr/spool/pcnfs. To change this to mode 755, do the following as root: chmod 755 /usr/spool/pcnfs C. A patch is available for the two vulnerabilities described in this advisory. Apply the patch using the GNU patch utility or by hand as necessary. Rebuild, reinstall, and restart rpc.pcnfsd. Set the mode of the top-level pcnfsd spool directory to 755. For example, in the version of pcnfsd cited in Section B, the top level spool directory is /usr/spool/pcnfs. To change this to mode 755, do the following as root: chmod 755 /usr/spool/pcnfs Below is the location of a version of the patch that is an improvement over the patch originally cited in the advisory. The modifications are in the suspicious() function in pcnfsd_misc.c., courtesy of Sun Microsystems, Inc. To prevent any confusion concerning the checksums, please see the file README.pcnfsd.93.02.16-cert. Checksums are also included below: ftp://info.cert.org/pub/tools/pcnfsd/README.pcnfsd.93.02.16-cert MD5 (README.pcnfsd.93.02.16-cert) = 07c64cd714bfaab3eb3849439a615b79 ftp://info.cert.org/pub/tools/pcnfsd/pcnfsd.93.02.16-cert-dist.tar.Z MD5 (pcnfsd.93.02.16-cert-dist.tar.Z) = dc9b50172dfba8e6f9ad0c83f0e087e8 Note: When the above file is unpacked, the md5 checksum referenced in the README.pcnfsd.93.02.16-cert matches the following: MD5 (pcnfsd.93.02.16-cert.tar) = 3a33f392d66b166cbc630275d8aba6f7 ftp://info.cert.org/pub/tools/pcnfsd/pcnfsd_misc.c-diffs MD5 (pcnfsd_misc.c-diffs) = e9a83e6d540ab4683767ecf6d66dda9d ftp://info.cert.org/pub/tools/pcnfsd/pcnfsd_print.c-diffs MD5 (pcnfsd_print.c-diffs) = 7d9dac3c14b258e855517894e2934b14 ......................................................................... Appendix A: Vendor Information Below is information we have received from vendors concerning the vulnerability described in this advisory. If you do not see your vendor's name, please contact the vendor directly for information. Berkeley Software Design, Inc. (BSDI) ===================================== The problem described in these vulnerabilities is present in all versions of BSD/OS. There is a patch (our patch number U210-007) for our 2.1 version of BSD/OS and associated products available from our patch and ftp servers or ftp://ftp.BSDI.COM/bsdi/patches/patches-2.1/U210-007 Data Design Systems, Inc. ========================= The Tandem NonStop Kernel (NSK) system, does NOT contain either of the vulnerabilities cited in the advisory. Digital Equipment Corporation ============================= For updated information, please refer to the Digital Equipment Corporation Vendor Bulletin #96.0383, available in ftp://info.cert.org/pub/vendors/dec/dec_96.0383 Note: Non-contract/non-warranty customers should contact local Digital support channels for information regarding these kits. As always, Digital urges you to periodically review your system management and security procedures. Digital will continue to review and enhance the security features of its products and work with customers to maintain and improve the security and integrity of their systems. FreeBSD Inc. =========== There are two seperate ways of upgrading. The patch listed below is a source code patch, and is available from: ftp://ftp.FreeBSD.ORG/pub/FreeBSD/FreeBSD-current/ports/net/pcnfsd/patches/patch-ad MD5 (patch-ad) = 6dfdf6229632e53cb060961ac09bbd1a This is part of the ports collection and anyone using current revisions of the ports system will automatically have this patch applied. You can also get a FreeBSD "package" (pre-compiled binary) from: ftp://ftp.FreeBSD.ORG/pub/FreeBSD/packages-current/net/pcnfsd-93.02.16.tgz MD5 (pcnfsd-93.02.16.tgz) = 59c54dae46d1b4fd41887877b0a7097a Hewlett-Packard Company ======================= 1. The rpc.pcnfsd binary that ships with HP systems contains a vulnerability that could allow a user to change permissions on a restricted file or directory. Hewlett Packard is delivering a set of operating system dependent patches which contain a new version of rpc.pcnfsd. Accompanying each patch is a README file which discusses the general purpose of the patch and describes how to apply it to your system. Recommended solution: Apply one of the following patches based on your system hardware and operating system revision: s300/s400 9.X - PHNE_7371 (rpc.pcnfsd) s700/s800 9.X - PHNE_7072 (NFS Megapatch) s700/s800 10.X - PHNE_7073 (NFS Megapatch) The patches described above provide a new version of the rpc.pcnfsd executable which fixes the vulnerability. 2. The rpc.pcnfsd binary that ships with most Unix systems contains a vulnerability that could allow users to execute arbitrary commands on the machine where pcnfsd runs. The rpc.pcnfsd daemon that ships with Hewlett Packard systems does not make the system call that allows this vulnerability. Since HP systems are not vulnerable - there is no fix! To subscribe to automatically receive future NEW HP Security Bulletins please refer to information in ftp://info.cert.org/pub/vendors/hp/HP.contact_info IBM Corporation =============== See the appropriate release below to determine your action. AIX 3.2 ------- Apply the following fixes to your system: APAR - IX57623 (PTF - U442633) APAR - IX56965 (PTF - U442638) To determine if you have these PTFs on your system, run the following commands: lslpp -lB U442633 lslpp -lB U442638 AIX 4.1 ------- Apply the following fixes to your system: APAR - IX57616 APAR - IX56730 To determine if you have these APARs on your system, run the following commands: instfix -ik IX57616 instfix -ik IX56730 To Order -------- APARs may be ordered using FixDist or from the IBM Support Center. For more information on FixDist, reference URL: http://service.software.ibm.com/aixsupport/ or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist". IBM and AIX are registered trademarks of International Business Machines Corporation. NEC Corporation =============== Some systems are vulnerable and patches are available through anonymous FTP from ftp://ftp.meshnet.or.jp in the /pub/48pub/security directory. UP-UX/V (Rel4.2MP) R5.x NECu5s003.COM.pkg /pub/48pub/security/up/r5/pkg Results of sum = 3060 266 md5 = 79E626B99A55FB0DBCE6EE642874570A R6.x NECu6s003.COM.pkg /pub/48pub/security/up/r6/pkg Results of sum = 47304 272 md5 = 9FC9E993A5AB51291BF4817D3D70FBFD R7.x NECu7s003.COM.pkg /pub/48pub/security/up/r7/pkg Results of sum = 46470 291 md5 = 59CA6887078AF88EA165AFD3BF5A1374 EWS-UX/V(Rel4.2) R7.x NECe7s004.COM.pkg /pub/48pub/security/ews/r7/pkg Results of sum = 3827 194 md5 = 4D40D9258DAB7EA41C30789609818330 R8.x NECe8s004.COM.pkg /pub/48pub/security/ews/r8/pkg Results of sum = 24399 199 md5 = 40B4CB1140791C14D1B604B6E8CB5FCB R9.x(except EWS4800/110N) NECe9s008.COM.pkg /pub/48pub/security/ews/r9/pkg Results of sum = 23250 203 md5 = 5AD8BED137AAE7D0067EF3120574786C R9.x(EWS4800/110N) NECe9s007.COM.pkg /pub/48pub/security/ews/r9n/pkg Results of sum = 3972 201 md5 = 28B2FA99F5200F81C5465571EF27E08B R10.x NECeas004.COM.pkg /pub/48pub/security/ews/ran/pkg Results of sum = 51969 205 md5 = B6E12017E66DC8DC38FBE78CA1F0B0F0 EWS-UX/V (Rel4.2MP) R10.x NECmas007.COM.pkg /pub/48pub/security/ews/ra/pkg Results of sum = 48060 291 md5 = 42F8AE832071F033E21D8718A3670D76 UX/4800 R11.x NECmbs010.COM.pkg /pub/48pub/security/ews/rb/pkg Results of sum = 24885 335 md5 = 7A14CBE4EA9B2470E340B5EEFD523F95 For further information contact: UX48-security-support@nec.co.jp. We encourage you contact the vendor directly if you have any questions. NeXT Software, Inc. =================== NEXTSTEP is vulnerable. This will be fixed in the 4.0 release of OpenStep for Mach (aka NEXTSTEP 4.0, due out 2Q96). Novell ====== CERT staff do not know whether Novell's enhanced version of PCNFSD (LWPNFSD) is vulnerable to this problem. We encourage you contact the vendor directly if you have any questions. The Santa Cruz Operation, Inc. ============================== Patches for pcnfsd are currently being developed for the following releases: SCO OpenServer 5 SCO UnixWare 2.1. These releases, as well as all prior releases, are vulnerable to both issues mentioned in the advisory. Should you not need to use pcnfs, SCO recommends that you not run pcnfsd. This can be done by commenting out pcnfsd in the appropriate script that starts pcnfsd, located in /etc/rc2.d. This CERT advisory will be updated when further patch information is available. Silicon Graphics Corporation ============================ pcnfsd was only released for IRIX 5.3 and IRIX 6.2. SGI is producing patch1179 for IRIX 5.3. IRIX 6.2 is not vulnerable. Sun Microsystems, Inc. ====================== Sun has made patches available: Solaris 2.4, 2.5 (Sparc) 103095-02 Solaris 2.4, 2.5 (X86) 103457-01 SunOS 4.1.X 103096-02 TGV Software, Inc./Cisco Systems, Inc. ====================================== These vulnerabilities are UNIX-specific and are not present in any version of MultiNet for OpenVMS. - --------------------------------------------------------------------------- The CERT Coordination Center thanks Josh Daymont, Ben G., and Alfred H. of Avalon Security Research for providing information for this advisory. We thank Wolfgang Ley of DFN-CERT for his help in understanding these problems. - --------------------------------------------------------------------------- If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in the Forum of Incident Response and Security Teams (FIRST). We strongly urge you to encrypt any sensitive information you send by email. The CERT Coordination Center can support a shared DES key and PGP. Contact the CERT staff for more information. Location of CERT PGP key ftp://info.cert.org/pub/CERT_PGP.key CERT Contact Information - ------------------------ Email cert@cert.org Phone +1 412-268-7090 (24-hour hotline) CERT personnel answer 8:30-5:00 p.m. EST (GMT-5)/EDT(GMT-4), and are on call for emergencies during other hours. Fax +1 412-268-6989 Postal address CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 USA CERT publications, information about FIRST representatives, and other security-related information are available for anonymous FTP from http://www.cert.org/ ftp://info.cert.org/pub/ CERT advisories and bulletins are also posted on the USENET newsgroup comp.security.announce To be added to our mailing list for CERT advisories and bulletins, send your email address to cert-advisory-request@cert.org Copyright 1996 Carnegie Mellon University This material may be reproduced and distributed without permission provided it is used for noncommercial purposes and the copyright statement is included. * Registered U. S. Trademark and Patent Office. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Revision history Apr. 03, 1997 Minor changes: corrected a name in the acknowledgments; indicated that CERT is now a registered service mark Aug. 30, 1996 Information previously in the README was inserted into the advisory. Appendix B was moved to Sec. III.C. Appendix A - updated IBM URL in "To Order" section. Aug. 01, 1996 Appendix A - updated Hewlett-Packard patch information. July 26, 1996 Appendix A - modified NEC patch information. July 5, 1996 Appendix A - added pointer to updated vendor information for Digital Equipment Corporation. June 26, 1996 Appendix A - updated vendor information for NEC. Appendix A - added vendor information for Data Design Systems, Inc. May 8, 1996 Appendix A - added patch information for FreeBSD. May 6, 1996 Section II -added additional clarification about the impact of the vulnerability described. Appendix B - replaced the patch information originally contained in Appendix B with updated information. Appendix A - added updates for Digital Equipment Corporation, Novell, Sun Microsystems, Inc, and TGV Software, Inc./Cisco Systems, Inc. Apr. 23, 1996 Appendix A - added information from NEC Corporation. Apr. 19, 1996 Appendix B - new information on the fix referred to in Appendix B of the advisory. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBM0PT7HVP+x0t4w7BAQHq5AP/Yu2kYH1YEe3+mH41JpHR4qGAm9PpWFH3 jc7Mwgr2ablylKgcglIXQKI04MfPjLM1jXggjR1kHvKC4vg7UVhm9D5QlpKwduO1 r9mQbXSZJPRhUYlIjMGc3HB/raH6e7SbGdh9q/aRquJxwuqqA1AY+S0SSPza8YZw AoS2huUKXTo= =1nrN -----END PGP SIGNATURE-----