-----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN SGI IRIX ordist, login/scheme Buffer Overrun Vulnerability May 28, 1997 18:00 GMT Number H-62 ______________________________________________________________________________ PROBLEM: Two vulnerabilities have been identified on the SGI IRIX operating system: (1) ordist program, and the (2) login program. PLATFORM: All SGI systems running IRIX 6.2. Other versions (including IRIX 5.x) may be vulnerable. DAMAGE: These vulnerabilities may allow local users to gain root privileges. SOLUTION: Apply the suggested workarounds listed below. ______________________________________________________________________________ VULNERABILITY Exploit information involving these vulnerabilities have been ASSESSMENT: made publicly available. ______________________________________________________________________________ [ Start AUSCERT Advisories ] 1. ordist Buffer Overrun Vulnerability =========================================================================== AA-97.23 AUSCERT Advisory SGI IRIX ordist Buffer Overrun Vulnerability 28 May 1997 Last Revised: -- - ---------------------------------------------------------------------------- AUSCERT has received information that a vulnerability exists in ordist(1c), distributed under IRIX 6.2. Other versions of IRIX may also be vulnerable. 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 ordist(1c) is a program used to maintain identical copies of files over multiple hosts. It preserves the owner, group, mode and mtime of a file if possible. Due to insufficient bounds checking on arguments which are supplied by users, it is possible to overwrite the internal stack space of the ordist program while it is executing. By supplying a carefully designed argument to the ordist program, intruders may be able to force ordist to execute arbitrary commands. As ordist is setuid root, this may allow intruders to run arbitrary commands with the privileges of root. Sites can determine if this program is installed by using: % ls -l /usr/bsd/ordist ordist is installed by default in /usr/bsd. Sites are encouraged to check for the presence of this program regardless of the version of IRIX installed. Exploit information involving this vulnerability has been made publicly available. 2. Impact This vulnerability may allow local users to gain root privileges. 3. Workarounds/Solution AUSCERT recommends that sites prevent the exploitation of this vulnerability in ordist by immediately applying the workaround given in Section 3.1. If the ordist functionality is required by non-root users, AUSCERT recommends applying the workaround given in Section 3.2. Currently there are no vendor patches available that address this vulnerability. AUSCERT recommends that official vendor patches be installed when they are made available. 3.1 Remove setuid and non-root execute permissions To prevent the exploitation of the vulnerability described in this advisory, AUSCERT recommends that the setuid permissions be removed from the ordist program immediately. As ordist will no longer work for non-root users, it is recommended that the execute permissions for them also be removed. # ls -l /usr/bsd/ordist -rwsr-xr-x 1 root sys 70564 Nov 28 15:07 /usr/bsd/ordist # chmod 500 /usr/bsd/ordist # ls -l /usr/bsd/ordist -r-x------ 1 root sys 70564 Nov 28 15:07 /usr/bsd/ordist 3.2 Install ordist wrapper AUSCERT has developed a wrapper to help prevent programs from being exploited using the vulnerability described in this advisory. Sites which have a C compiler can obtain the source, compile and install the wrapper as described in Section 3.2.1. For sites without a C compiler, AUSCERT has made pre-compiled binaries available (Section 3.2.2). 3.2.1 Installing the wrapper from source The source for the wrapper, including installation instructions, can be found at: ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/ overflow_wrapper.c This wrapper replaces the ordist program and checks the length of the command line arguments which are passed to it. If an argument exceeds a certain predefined value (MAXARGLEN), the wrapper exits without executing the ordist command. The wrapper program can also be configured to syslog any failed attempts to execute ordist with arguments exceeding MAXARGLEN. For further instructions on using this wrapper, please read the comments at the top of overflow_wrapper.c. When compiling overflow_wrapper.c for use with ordist, AUSCERT recommends defining MAXARGLEN to be 32. The MD5 checksum for the current version of overflow_wrapper.c can be retrieved from: ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/CHECKSUM The CHECKSUM file has been digitally signed using the AUSCERT PGP key. 3.2.2 Installing the wrapper binaries A pre-compiled wrapper binary is provided for sites that wish to install the wrapper but do not have a C compiler available. AUSCERT has compiled the wrapper on IRIX 5.3, however later versions of IRIX should be able to use the wrapper binary without recompilation. The following compile time options have been used to create the binaries: REAL_PROG='"/usr/bsd/ordist.real"' MAXARGLEN=32 SYSLOG More information on these options can be found in Section 3.2.1 and in the overflow_wrapper.c source code. The pre-compiled binary for the wrapper program can be retrieved from: ftp://ftp.auscert.org.au/pub/auscert/tools/ AA-97.23-ordist_wrapper.tar.Z The MD5 checksum for AA-97.23-ordist_wrapper.tar.Z is: MD5 (AA-97.23-ordist_wrapper.tar.Z) = 0eed9d9a52658181a1ce9b4ce2ed7fd2 AA-97.23-ordist_wrapper.tar.Z contains a README file with installation instructions, as well as a pre-compiled binary. Sites are encouraged to carefully read the installation notes in the README file before installation. 4. Additional measures 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 ordist program is not needed by many sites. If sites had previously disabled this program, they would not have been susceptible to this latest vulnerability. - ---------------------------------------------------------------------------- 2. login/scheme Buffer Overrun Vulnerability =========================================================================== AA-97.22 AUSCERT Advisory SGI IRIX login/scheme Buffer Overrun Vulnerability 28 May 1997 Last Revised: -- - ---------------------------------------------------------------------------- AUSCERT has received information that a vulnerability exists in login(1), distributed under IRIX 6.2. Other versions (including IRIX 5.x) may also be vulnerable. 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 login(1) is a program used at the beginning of each terminal session that allows users to identify themselves to the session. Under current versions of IRIX this functionality is supplied by the program /usr/lib/iaf/scheme. The login program is a symbolic link to /usr/lib/iaf/scheme. Due to insufficient bounds checking on arguments which are supplied by users, it is possible to overwrite the internal stack space of the scheme program while it is executing. By supplying a carefully designed argument to the scheme program, intruders may be able to force scheme to execute arbitrary commands. As scheme is setuid root, this may allow intruders to run arbitrary commands with root privileges. The login program is installed in /usr/bin/login. Under default configurations this is a symbolic link to /usr/lib/iaf/scheme. % ls -l /usr/bin/login lrwxr-xr-x 1 root sys 17 Nov 22 1994 /usr/bin/login -> ../lib/iaf/scheme % ls -l /usr/lib/iaf/scheme -rwsr-xr-x 1 root sys 65832 Nov 22 1994 /usr/lib/iaf/scheme Exploit information involving this vulnerability has been made publicly available. Although AUSCERT has only verified this vulnerability under IRIX 6.2, this vulnerability is believed to affect other versions of IRIX, including IRIX 5.x. 2. Impact This vulnerability may allow local users to gain root privileges. 3. Workarounds/Solution AUSCERT recommends that sites prevent the exploitation of this vulnerability in login/scheme by immediately applying the workaround given in Section 3.1. To maintain the full login/scheme functionality, AUSCERT recommends applying the workaround given in Section 3.2. Currently there are no vendor patches available that address this vulnerability. AUSCERT recommends that official vendor patches be installed when they are made available. 3.1 Remove setuid and non-root execute permissions To prevent the exploitation of the vulnerability described in this advisory, AUSCERT recommends that the setuid permissions be removed from the scheme program immediately. # ls -l /usr/lib/iaf/scheme -rwsr-xr-x 1 root sys 58324 Nov 28 1996 /usr/lib/iaf/scheme # chmod 500 /usr/lib/iaf/scheme # ls -l /usr/lib/iaf/scheme -r-x------ 1 root sys 58324 Nov 28 1996 /usr/lib/iaf/scheme 3.2 Install scheme wrapper AUSCERT has developed a wrapper to help prevent programs from being exploited using the vulnerability described in this advisory. Sites which have a C compiler can obtain the source, compile and install the wrapper as described in Section 3.2.1. For sites without a C compiler, AUSCERT has made pre-compiled binaries available (Section 3.2.2). 3.2.1 Installing the wrapper from source The source for the wrapper, including installation instructions, can be found at: ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/ overflow_wrapper.c This wrapper replaces the scheme program and checks the length of the command line arguments which are passed to it. If an argument exceeds a certain predefined value (MAXARGLEN), the wrapper exits without executing the scheme command. The wrapper program can also be configured to syslog any failed attempts to execute scheme with arguments exceeding MAXARGLEN. For further instructions on using this wrapper, please read the comments at the top of overflow_wrapper.c. When compiling overflow_wrapper.c for use with scheme, AUSCERT recommends defining MAXARGLEN to be 32. The MD5 checksum for the current version of overflow_wrapper.c can be retrieved from: ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/CHECKSUM The CHECKSUM file has been digitally signed using the AUSCERT PGP key. 3.2.2 Installing the wrapper binaries A pre-compiled wrapper binary is provided for sites that wish to install the wrapper but do not have a C compiler available. AUSCERT has compiled the wrapper on IRIX 5.3, however later versions of IRIX should be able to use the wrapper binary without recompilation. The following compile time options have been used to create the binaries: REAL_PROG='"/usr/lib/iaf/scheme.real"' MAXARGLEN=32 SYSLOG More information on these options can be found in Section 3.2.1 and in the overflow_wrapper.c source code. The pre-compiled binaries for the wrapper program can be retrieved from: ftp://ftp.auscert.org.au/pub/auscert/tools/ AA-97.22-scheme_wrapper.tar.Z The MD5 checksum for AA-97.22-scheme_wrapper.tar.Z is: MD5 (AA-97.22-scheme_wrapper.tar.Z) = dc302aa275a4009d1545180bfce8ebf4 AA-97.22-scheme_wrapper.tar.Z contains a README file with installation instructions, as well as a pre-compiled binary. Sites are encouraged to carefully read the installation notes in the README file before installation. - ---------------------------------------------------------------------------- [ End AUSCERT Advisories ] ______________________________________________________________________________ CIAC wishes to acknowledge the contributions of AUSCERT, Ian Farquhar, and the Prentice Center, University of Queensland for 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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