__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN suidperl Vulnerability June 28, 1996 17:00 GMT Number G-28a ______________________________________________________________________________ PROBLEM: A vulnerability has been discovered in systems that contain the suidperl program and that support saved set_user_ID and saved set_group_ID. PLATFORM: Any system that Perl versions 4 and 5 can be compiled and installed in such a way that they will be vulnerable. DAMAGE: By exploiting this vulnerability, anyone with access to an account on such a system may gain root access. SOLUTION: Install the proper patches and/or use the workarounds provided below. ______________________________________________________________________________ VULNERABILITY Knowledge of how to exploit these vulnerabilities are becoming ASSESSMENT: widely known. ______________________________________________________________________________ CIAC has obtained information from CERT pertaining to vulnerabilities in systems that contain the suidperl program and that support saved set_user_ID and saved set_group_ID. CIAC recommends that you install the proper patch and/or follow the solutions described below. ______________________________________________________________________________ [Begin CERT Bulletin] The CERT Coordination Center has received reports of a vulnerability in systems that contain the suidperl program and that support saved set-user-ID and saved set-group-ID. By exploiting this vulnerability, anyone with access to an account on such a system may gain root access. Saved set-user-IDs and set-group-IDs are sometimes referred to as POSIX saved IDs. suidperl is also known as sperl followed by a version number, as in sperl5.002. Perl versions 4 and 5 can be compiled and installed in such a way that they will be vulnerable on some systems. If you have installed the suidperl or sperl programs on a system that supports saved set-user-ID and set-group-ID, you may be at risk. The CERT Coordination Center recommends that you first disable the suidperl and sperl programs (Section III.A). If you need the functionality, we further recommend that you either apply a patch for this problem or install Perl version 5.003 (Section III.B). If neither a patch nor a new version are viable alternatives, we recommend installing the wrapper written by Larry Wall as a workaround for this problem (Section III.C). As we receive additional information relating to this advisory, we will place it in ftp://info.cert.org/pub/cert_advisories/CA-96.12.README We encourage you to check our README files regularly for updates on advisories that relate to your site. - ----------------------------------------------------------------------------- I. Description On some systems, setuid and setgid scripts (scripts written in the C shell, Bourne shell, or Perl, for example, with the set user or group ID permissions enabled) are insecure due to a race condition in the kernel. For those systems, Perl versions 4 and 5 attempt to work around this vulnerability with a special program named suidperl, also known as sperl. Even on systems that do provide a secure mechanism for setuid and setgid scripts, suidperl may also be installed--although it is not needed. suidperl attempts to emulate the set-user-ID and set-group-ID features of the kernel. Depending on whether the script is set-user-ID, set-group-ID, or both, suidperl achieves this emulation by first changing its effective user or group ID to that of the original Perl script. suidperl then reads and executes the script as that effective user or group. To do these user and group ID changes correctly, suidperl must be installed as set-user-ID root. On systems that support saved set-user-ID and set-group-ID, suidperl does not properly relinquish its root privileges when changing its effective user and group IDs. II. Impact On a system that has the suidperl or sperl program installed and that supports saved set-user-ID and saved set-group-ID, anyone with access to an account on the system can gain root access. III. Solution The command in Section A helps you determine if your system is vulnerable and, if it is, optionally disables the suidperl and sperl programs that it locates. After you have run this command on all of your systems, your system will no longer be vulnerable. If you find that your system is vulnerable, then you need to replace the suidperl and sperl programs with new versions. Section B describes how to do that. Finally, Section C identifies a wrapper that can be used in place of the suidperl program. A. How to determine if your system is vulnerable To determine if a system is vulnerable to this problem and to disable the programs that are believed to be vulnerable, use the following find command or a variant. Consult your local system documentation to determine how to tailor the find program on your system. You will need to run the find command on each system you maintain because the command examines files on the local disk only. Substitute the names of your local file systems for FILE_SYSTEM_NAMES in the example. Example local file system names are /, /usr, and /var. You must do this as root. Note that this is one long command, though we have separated it onto three lines using back-slashes. find FILE_SYSTEM_NAMES -xdev -type f -user root \ \( -name 'sperl[0-9].[0-9][0-9][0-9]' -o -name \ 'suidperl' \) -perm -04000 -print -ok chmod ug-s '{}' \; This command will find all files on a system that are - only in the file system you name (FILE_SYSTEM_NAMES -xdev) - regular files (-type f) - owned by root (-user root) - named appropriately (-name 'sperl[0-9].[0-9][0-9][0-9]' -o -name 'suidperl') - setuid root (-perm -04000) Once found, those files will - have their names printed (-print) - have their modes changed, but only if you type `y' in response to the prompt (-ok chown ug-s '{}' \;) B. Obtain and install the appropriate patch according to the instructions included with the patch. Vendor information ------------------ Apple Computer, Inc. ==================== A/UX 3.1.1 and earlier support saved set-{user,group}-ids. A/UX 3.1.1 and earlier do not have Perl as part of the standard product. Data General Corporation ======================== Data General does support saved set-user-IDs and set-group-IDs on DG/UX. Data General does not ship suidperl or sperl* with DG/UX. Digital Equipment Corporation ============================= Digital UNIX and Digital's ULTRIX Operating systems do support saved suid and saved guid in the process context. Digital does not ship Perl with any operating system. Hewlett-Packard Company ======================= HP/UX versions 8.X, 9.X, and 10.X all support saved set-user-id. None of HP/UX versions 8.X, 9.X, and 10.X have Perl as part of the standard product. IBM Corporation =============== AIX versions 3.2.5 and 4.X support saved set-user-id. AIX versions 3.2.5 and 4.X do not have Perl as part of the standard product. However, the SP2's PSSP software does contain suidperl, but the program is not installed with the setuid bit set. Linux ===== Linux 1.2 and 2.0 support saved set-user-id. Most distributions of Linux provide suidperl and sperl. The fixsperl script works on linux, and it is recommended that this fix be applied until a new Perl release is made. Open Software Foundation ======================== OSF/1 1.3 or later support saved set-user-id OSF/1 1.3 or later does not have Perl as part of the standard product. Sony Corporation ================ NEWS-OS 4.X does not support saved set-user-id and therefore any version of Perl on that system is not vulnerable. NEWS-OS 6.X does support saved set-user-id. X.org ===== None of X.org's development systems are vulnerable to the saved set-user-IDs and set-group-IDs problems, and suidperl is not shipped with either of our products. Vendor patches -------------- You may be vulnerable if your vendor supports saved set-user-ID and set-group-ID and ships suidperl or sperl. You need to get a patched version from your vendor. Appendix A contains information provided by vendors as of the date of this advisory. When we receive updated information, we will put it in CA-96.12.README. Until you can install a patch, we recommend disabling suidperl. The find command above will help you do that. If you need suidperl or sperl, an alternative is to install the wrapper described in Section C. Source code patches ------------------- If you have installed Perl from source code, you should install source code patches. Patches are available from the CPAN (Comprehensive Perl Archive Network) archives. Patch for Perl Version 4: File src/fixsuid4-0.pat MD5 Checksum af3e3c40bbaafce134714f1381722496 Patch for Perl Version 5: File src/fixsuid5-0.pat MD5 Checksum 135c96ee400fd37a38a7ef37edd489e9 In addition, Perl version 5.003 contains this patch, so installing it on your system also addresses this vulnerability. Perl 5.003 is available from the CPAN archives. Here are the specifics: File src/5.0/perl5.003.tar.gz MD5 Checksum b1bb23995cd25e5b750585bfede0e8a5 The CPAN archives can be found at the following locations: CPAN master site ftp://ftp.funet.fi/pub/languages/perl/CPAN/ Africa ftp://ftp.is.co.za/programming/perl/CPAN/ Asia ftp://dongpo.math.ncu.edu.tw/perl/CPAN/ ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/ Australasia ftp://coombs.anu.edu.au/pub/perl/ ftp://ftp.mame.mu.oz.au/pub/perl/CPAN/ ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/ Europe ftp://ftp.arnes.si/software/perl/CPAN/ ftp://ftp.ci.uminho.pt/pub/lang/perl/ ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/ ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/ ftp://ftp.funet.fi/pub/languages/perl/CPAN/ ftp://ftp.ibp.fr/pub/perl/CPAN/ ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/ ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/ ftp://ftp.rz.ruhr-uni-bochum.de/pub/programming/languages/perl/CPAN/ ftp://ftp.sunet.se/pub/lang/perl/CPAN/ ftp://ftp.switch.ch/mirror/CPAN/ ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/ North America ftp://ftp.cis.ufl.edu/pub/perl/CPAN/ ftp://ftp.delphi.com/pub/mirrors/packages/perl/CPAN/ ftp://ftp.sedl.org/pub/mirrors/CPAN/ ftp://ftp.sterling.com/programming/languages/perl/ ftp://ftp.uoknor.edu/mirrors/CPAN/ ftp://uiarchive.cso.uiuc.edu/pub/lang/perl/CPAN/ C. If you need setuid or setgid Perl scripts and are unable to apply the source code patches listed in Section B, we suggest that you retrieve Larry Wall's fixsperl script noted below. fixsperl is a script that replaces the suidperl and sperl programs with a wrapper that eliminates the vulnerability. The script is available from the CPAN archives as File src/fixsperl-0 MD5 Checksum f13900d122a904a8453a0af4c1bdddc6 Note that this script should be run one time, naming every suidperl or sperl file on your system. If you add another version of suidperl or sperl to your system, then you must run fixsperl on those newly installed versions. _______________________________________________________________________________ The CERT Coordination Center staff thanks Paul Traina, Larry Wall, Eric Allman, Tom Christiansen, and AUSCERT for their support in the development of this advisory. _______________________________________________________________________________ [End CERT Bulletin] CIAC has received additional information from FreeBSD, Inc. regarding the suidperl vulnerability. [Start FreeBSD Bulletin] ============================================================================= FreeBSD-SA-96:12 Security Advisory FreeBSD, Inc. Topic: security compromise from perl (suidperl) utility Category: core and ports Module: perl Announced: 1996-06-28 Affects: FreeBSD 2.0, 2.0.5, 2.1, 2.1-stable, and 2.2-current Corrected: 2.1-stable and 2.2-current as of 1996-06-03 FreeBSD only: no Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:12/ ============================================================================= I. Background FreeBSD ships perl version 4 as part of the base level system, in addition, a port for perl version 5 is also provided with a similar vulnerability. The vulnerability is specific to the suidperl flavors of perl installed on the system. This problem is present in all source code and binary distributions of FreeBSD version 2.0.5 and later released before 1996-05-21. This problem is not present in FreeBSD 2.0 and earlier versions of FreeBSD. II. Problem Description The authors of perl provide a "suidperl" program for proper processing of setuid perl scripts on systems where race conditions where setuid scripts could be exploited to gain unauthorized access. FreeBSD installs this suidperl program (and a link) as part of the standard installation. However, privilege processing done by this program does not take into account recent functionality extensions in the seteuid/setegid system calls. III. Impact This vulnerability can only be exploited by users with a valid account on the local system to easily obtain superuser access. This vulnerability is present on all systems with the _POSIX_SAVED_IDS functionality extension where suidperl has been installed. IV. Workaround One may simply disable the setuid bit on all copies of the setuid version of perl. This will close the vulnerability but render inoperable setuid perl scripts. No software currently shipping as part of FreeBSD relies on this functionality so the impact is only to third party software. As root, execute the commands: # chmod 111 /usr/bin/suidperl # chmod 111 /usr/bin/sperl4.036 In addition, if you have installed the perl5 port: # chmod 111 /usr/local/bin/suidperl # chmod 111 /usr/local/bin/sperl5.001 then verify that the setuid permissions of the files have been removed. The permissions array should read "-r-xr-xr-x" as shown here: # ls -l /usr/bin/s*perl* ---x--x--x 2 root bin 307200 Jun 1 17:16 /usr/bin/sperl4.036 ---x--x--x 2 root bin 307200 Jun 1 17:16 /usr/bin/suidperl and for the perl5 port: # ls -l /usr/local/bin/s*perl* ---x--x--x 2 root bin 397312 Jan 22 15:15 /usr/local/bin/sperl5.001 ---x--x--x 2 root bin 397312 Jan 22 15:15 /usr/local/bin/suidperl V. Solution *NOTE* A patch for perl is available directly from Larry Wall (the author of perl) which solves this vulnerability in a different fashion than the FreeBSD patches. You may apply either the FreeBSD patches, or Larry's patches, or both. The patches solve the problem via two different mechanisms. Patches are available which eliminate this vulnerability. The following patch should be applied to the system sources and suidperl should be rebuilt and reinstalled. Apply the patch, then: # cd /usr/src/gnu/usr.bin/perl/sperl # make depend # make all # make install A similar patch is also available for the perl5 port. Apply the following patch by moving it into the patch directory for the port distribution and rebuilding and installing perl5: # cd /usr/ports/lang/perl5 # cp /patch-a[ab] patches # make all # make install NOTE: These patches do NOT solve the vulnerability for FreeBSD 2.0 or 2.0.5. These only solve the problem for 2.1 and later. Patches specific to FreeBSD 2.0 and 2.0.5 are available at the URL listed at the top of this file. ============================================================================= FreeBSD, Inc. Web Site: http://www.freebsd.org/ Confidential contacts: security-officer@freebsd.org PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc Security notifications: security-notifications@freebsd.org Security public discussion: security@freebsd.org Notice: Any patches in this document may not apply cleanly due to modifications caused by digital signature or mailer software. Please reference the URL listed at the top of this document for original copies of all patches if necessary. ============================================================================= [End FreeBSD Bulletin] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of CERT, AUSCERT, Paul Traina, Larry Wall, Eric Allman, Tom Christiansen, FreeBSD, and all the other vendors who provided information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. 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LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) G-18: Digital OSF/1 dxconsole Security Vulnerability G-19: IBM AIX rmail Vulnerability G-20: Vulnerability in NCSA and Apache httpd Servers G-21: Vulnerabilities in PCNFSD Program G-22: rpc.statd Vulnerability G-23: Solaris NIS+ Configuration Vulnerability G-24: FreeBSD Security Vulnerabilities G-25: SUN statd Program Vulnerability G-26: IRIX Desktop Permissions Panel Vulnerability G-27: SCO Kernel Security Vulnerability RECENT CIAC NOTES ISSUED (Previous Notes available from CIAC) Notes 07 - 3/29/95 A comprehensive review of SATAN Notes 08 - 4/4/95 A Courtney update Notes 09 - 4/24/95 More on the "Good Times" virus urban legend Notes 10 - 6/16/95 PKZ300B Trojan, Logdaemon/FreeBSD, vulnerability in S/Key, EBOLA Virus Hoax, and Caibua Virus Notes 11 - 7/31/95 Virus Update, Hats Off to Administrators, America On-Line Virus Scare, SPI 3.2.2 Released, The Die_Hard Virus Notes 12 - 9/12/95 Securely configuring Public Telnet Services, X Windows, beta release of Merlin, Microsoft Word Macro Viruses, Allegations of Inappropriate Data Collection in Win95 Notes 96-01 - 3/18/96 Java and JavaScript Vulnerabilities, FIRST Conference Announcement, Security and Web Search Engines, Microsoft Word Macro Virus Update