=========================================================================== [8lgm]-Advisory-20.UNIX.SunOS-sendmailV5.1-Aug-1995 PROGRAM: sendmail(8) VULNERABLE VERSIONS: SunOS 4.1.* Sendmail v5 sources Potentially other vendor v5 based sendmails DESCRIPTION: The method used by sendmail version 5 to open a control file is insecure. A race condition exists whereby another process may obtain a control-file file descriptor, opened for write access. IMPACT: Local users can write their own control files, and run programs as any user, bar root. This increases chances of obtaining root access on the local system. REPEAT BY: A program to exploit this vulnerability is available as of now. This program has been tested with the latest Sun patch, and should work on other platforms. To obtain this program, send mail to 8lgm-fileserver@8lgm.org, with a line in the body of the message containing:- SEND grabfd.c DISCUSSION: Sendmail v5, during execution, sets umask(0), which is an insecure mask. In order not to leave open control files with mode 666, sendmail v5 uses chmod(2) to set a secure file mode. However this is a race condition, as we can obtain an open file descriptor for write by opening the control file before the call to chmod(2). WORKAROUND: Change the mode on /usr/spool/mqueue to 700. This will prevent normal users gaining access to the queue files directly. FIX: Contact vendor for fix. Patch source to use a more restrictive umask. STATUS UPDATE: The file: [8lgm]-Advisory-20.UNIX.SunOS-sendmailV5.1-Aug-1995.README will be created on www.8lgm.org. This will contain updates on any further versions which are found to be vulnerable, and any other information received pertaining to this advisory. ----------------------------------------------------------------------- FEEDBACK AND CONTACT INFORMATION: majordomo@8lgm.org (Mailing list requests - try 'help' for details) 8lgm@8lgm.org (Everything else) 8LGM FILESERVER: All [8LGM] advisories may be obtained via the [8LGM] fileserver. For details, 'echo help | mail 8lgm-fileserver@8lgm.org' 8LGM WWW SERVER: [8LGM]'s web server can be reached at http://www.8lgm.org. This contains details of all 8LGM advisories and other useful information. ===========================================================================