-----BEGIN PGP SIGNED MESSAGE----- =============================================================================== Security Advisory CERT-NL =============================================================================== Author/Source : Gert Meijerink Index : S-97-19 Distribution : World Page : 1 Classification: External Version: 1 Subject : Solaris 2.x eject Buffer Overrun Vulnerability Date : 17-mar-97 =============================================================================== By courtesy of AUSCERT we received information on a vulnerability in Solaris 2.x eject Buffer Overrun Vulnerability CERT-NL recommends that sites apply the workaround given in Section 3 until vendor patches are made available. =========================================================================== AA-97.10 AUSCERT Advisory Solaris 2.x eject Buffer Overrun Vulnerability 14 March 1997 Last Revised: -- - - --------------------------------------------------------------------------- AUSCERT has received information that a vulnerability exists in eject(1), distributed under Solaris 2.4, 2.5 and 2.5.1. Earlier versions may 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 eject(1) is a program used for those removable media devices that do not have a manual eject button, or for those that do, but are managed by Volume Management Due to insufficient bounds checking on arguments which are supplied by users, it is possible to overwrite the internal stack space of the eject program while it is executing. By supplying a carefully designed argument to the eject program, intruders may be able to force eject to execute arbitrary commands. As eject is setuid root, this may allow intruders to run arbitrary commands with root privileges. Sites can determine if this program is installed by using: % ls -l /usr/bin/eject eject is installed by default in /usr/bin. Sites are encouraged to check for the presence of this program regardless of the version of Solaris installed. Exploit information involving this vulnerability has been made publicly available. Sun Microsystems has informed AUSCERT that they are currently working on this vulnerability. 2. Impact Local users may gain root privileges. 3. Workarounds/Solution AUSCERT recommends that sites prevent the exploitation of this vulnerability in eject by immediately applying the workaround given in Section 3.1. If the eject functionality is required 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 eject program immediately. As eject will no longer work for non-root users, it is recommended that the execute permissions also be removed. # ls -l /usr/bin/eject -r-sr-xr-x 1 root other 5804 Mar 14 09:47 /usr/bin/eject # chmod 500 /usr/bin/eject # ls -l /usr/bin/eject -r-x------ 1 root other 5804 Mar 14 09:47 /usr/bin/eject 3.2 Install eject 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 for Solaris 2.4, 2.5 and 2.5.1 (Section 3.1.2). 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.c This wrapper replaces the eject 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 eject command. The wrapper program can also be configured to syslog any failed attempts to execute eject 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 eject, AUSCERT recommends defining MAXARGLEN to be 32. The MD5 checksum for Version 1.0 of overflow_wrapper.c is: MD5 (overflow_wrapper.c) = f7f83af7f3f0ec1188ed26cf9280f6db 3.2.2 Installing the wrapper binaries Pre-compiled wrapper binaries are provided for sites that wish to install the wrapper but do not have a C compiler available. AUSCERT has compiled the wrapper on Solaris 2.4, 2.5 and 2.5.1. The following compile time options have been used to the create the binaries: REAL_PROG='"/usr/bin/eject.real"' MAXARGLEN=32 SYSLOG More information on these options can be found in Section 3.1.1 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/eject_wrapper.tar.Z The MD5 checksum for eject_wrapper.tar.Z is: MD5 (eject_wrapper.tar.Z) = 1ae34aea7a637d6464105cbec7ff4443 eject_wrapper.tar.Z contains a README file with installation instructions, as well as pre-compiled binaries for Solaris 2.4, 2.5 and 2.5.1. The binaries have been linked statically so they are larger than the default eject 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 vulnerability 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 eject program is not needed by many sites. If sites had previously disabled this program, they would not have been susceptible to this latest vulnerability. - - --------------------------------------------------------------------------- AUSCERT thanks Brian Meilak (Queensland University of Technology) and Sun Microsystems for their assistance in this matter. - - --------------------------------------------------------------------------- ============================================================================== CERT-NL is the Computer Emergency Response Team for SURFnet customers. SURFnet is the Dutch network for educational, research and related institutes. CERT-NL is a member of the Forum of Incident Response and Security Teams (FIRST). All CERT-NL material is available under: In case of computer or network security problems please contact your local CERT/security-team or CERT-NL (if your institute is NOT a SURFnet customer please address the appropriate (local) CERT/security-team). 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