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-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2004.0116 -- iDEFENSE Security Advisory 02.10.04 XFree86 Font Information File Buffer Overflow 11 February 2004 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: XFree86 Publisher: iDEFENSE Operating System: UNIX Linux Mac OS X OS/2 Impact: Root Compromise Access Required: Existing Account CVE Names: CAN-2004-0083 - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 iDEFENSE Security Advisory 02.10.04 XFree86 Font Information File Buffer Overflow http://www.idefense.com/application/poi/display?id=72 February 10, 2004 I. BACKGROUND In short, XFree86 is an open source X11-based desktop infrastructure. XFree86, provides a client/server interface between display hardware (the mouse, keyboard, and video displays) and the desktop environment while also providing both the windowing infrastructure and a standardized application interface (API). XFree86 is platform independent, network-transparent and extensible. II. DESCRIPTION Exploitation of a buffer overflow in The XFree86 Project Inc.'s XFree86 X Window System allows local attackers to gain root privileges. The problem specifically exists in the parsing of the 'font.alias' file. The X server (running as root) fails to check the length of user provided input. A malicious user may craft a malformed 'font.alias' file causing a buffer overflow upon parsing, eventually leading to the execution of arbitrary code. - - - - From XFree86-4.2.1/xc/lib/font/fontfile/dirfile.c: ReadFontAlias(char *directory, Bool isFile, FontDirectoryPtr *pdir) { char alias[MAXFONTNAMELEN]; The above code sets up the buffer that will be exploited directly in front of the frame pointer and return address. while (status == Successful) { token = lexAlias(file, &lexToken); lexAlias() reads an arbitrary length token from file, and returns a pointer to it in &lexToken, without performing any bounds checking. It then returns NAME when it reaches whitespace. switch (token) { case NAME: strcpy(alias, lexToken); If lexToken is longer than MAXFONTNAMELEN (1024 chars) an overflow occurs. To reproduce the overflow on the command line: # cat > fonts.dir <<EOF 1 word.bdf -misc-fixed-medium-r-semicondensed--13-120-75-75-c-60-iso8859-1 EOF # perl -e 'print "0" x 1024 . "A" x 96 . "\n"' > fonts.alias # X :0 -fp $PWD {Some output removed} Caught signal 11. Server aborting... eip: 41414141 eflags: 00003282 {Some output removed} Code: Segmentation fault (core dumped) # III. ANALYSIS Successful exploitation requires that an attacker be able to execute commands in the X11 subsystem. This can be done either by having console access to the target or through a remote exploit against any X client program such as a web-browser, mail-reader or game. Successful exploitation yields root access. IV. DETECTION iDEFENSE has confirmed the existence of this vulnerability in XFree86 versions 4.1.0 to the current version 4.3.0. It is suspected that earlier versions are vulnerable as well. V. VENDOR RESPONSE The patch for the problem is at ftp://ftp.xfree86.org/pub/XFree86/4.3.0/fixes/fontfile.diff and it is applicable to all affected XFree86 versions. The change log entry is: 794. Fix font alias overrun. See also http://www.xfree86.org/cvs/changes/ for changelog extracts for the trunk and several branches. The patch has been applied to the trunk and all of the 4.x release branches. VI. CVE INFORMATION The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project has assigned CAN-2004-0083 to this issue. VII. DISCLOSURE TIMELINE January 9, 2004 Exploit acquired by iDEFENSE February 3, 2004 Vendor notified February 3, 2004 Response received from David Dawes at XFree86.org February 4, 2004 iDEFENSE clients notified February 10, 2004 Public disclosure VIII. CREDIT Greg MacManus (iDEFENSE Labs) is credited with the discovery of this vulnerability. - -----BEGIN PGP SIGNATURE----- Version: PGP 8.0.3 iQA/AwUBQCkyufrkky7kqW5PEQLonACfXr39VTFMM0siQ9qQG4ujRXKSTggAoLKi gdS6+/EbfSpKM3TX1tzCsNfX =F0Tw - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. 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Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/render.html?cid=1980 If you believe that your computer system has been compromised or attacked in any way, we encourage you to let us know by completing the secure National IT Incident Reporting Form at: http://www.auscert.org.au/render.html?it=3192 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQCVAwUBQCmGeSh9+71yA2DNAQEWJAP/eJa5ApkpmdcxjyDtR/S3g9j8vnOAQbsY +UuSozOI0CsqzCDGGLDFTaWOspsFWSEvh56+q6RDD7+sSyoHjjUBG+4Y9Nz06VPM bMFzfsZy4fcsFqfXB+oNaoT8Sr21V1w8z3vK9CXpQzqtSlnkrpwMfFOJngVE39Jc mZtA4NSSX+8= =ST1m -----END PGP SIGNATURE-----