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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2005.0879 -- iDEFENSE Security Advisory 11.04.05 Clam AntiVirus Cabinet-file handling Denial of Service Vulnerability 7 November 2005 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Clam AntiVirus 0.86.1 Publisher: iDEFENSE Operating System: Mac OS X UNIX variants Windows Impact: Denial of Service Access: Remote/Unauthenticated Original Bulletin: http://www.idefense.com/application/poi/display?id=334 - --------------------------BEGIN INCLUDED TEXT-------------------- Clam AntiVirus Cabinet-file handling Denial of Service Vulnerability iDEFENSE Security Advisory 11.04.05 http://www.idefense.com/application/poi/display?type=vulnerabilities November 4, 2005 I. BACKGROUND Clam AntiVirus is a GPL anti-virus toolkit for Unix. II. DESCRIPTION Remote exploitation of a design error in Clam AntiVirus ClamAV allows attackers to cause a denial of service (DoS) condition. The vulnerability specifically exists with the libmspack library, which is included in ClamAV. The vulnerability can be found in the cabd_find function within mspack/cabd.c: for (offset = 0; offset < flen; offset += length) { length = flen - offset; [... read length from file ...] for (p = &buf[0], pend = &buf[length]; p < pend; ) { switch (state) { [ ... ] case 19: => header has been completely read, cablen has been read from bytes 8-11 [...] /* likely cabinet found -- try reading it */ cab = sys->alloc(sys, sizeof(struct mscabd_cabinet_p); => an mscabd_cabinet_p entry will be allocated each time /* cabinet read correctly! */ offset = caboff + cablen; => if cablen (and caboff) == 0, offset will be equal to 0 [...] /* restart search */ [...] length = 0; p = pend; state = 0; => if offset == 0, we will restart at the beginning of the file => (because length == 0, so offset will still be zero in the next iteration) break; } } } If this function is called with a length value of zero, an infinite loop occurs. The comments above explain the scenario. III. ANALYSIS Successful exploitation requires an attacker to send a specially constructed CAB file through a mail gateway or personal anti-virus client utilizing the ClamAV scanning engine. The infinite loop will cause the ClamAV software to use all available processor resources, resulting in a denial of service or severe degradation of system performance. Ultimately, the OOM handler will terminate a task in order to alleviate the stress on the system. IV. DETECTION iDEFENSE has confirmed this vulnerability on ClamAV 0.86.1. All previous versions are suspected vulnerable to this issue. V. WORKAROUND Archive file analysis can be disabled (--no-archive) but this can have severe impacts on the virus detection functionality. VI. VENDOR RESPONSE The vendor has released clamav 0.87.1 to address this vulnerability. It is available for download at: http://prdownloads.sourceforge.net/clamav/clamav-0.87.1.tar.gz?download VII. CVE INFORMATION A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet. VIII. DISCLOSURE TIMELINE 10/07/2005 Initial vendor notification 10/12/2005 Initial vendor response 11/04/2005 Coordinated public disclosure IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous. Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp Free tools, research and upcoming events http://labs.idefense.com X. LEGAL NOTICES Copyright (c) 2005 iDEFENSE, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDEFENSE. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice@idefense.com for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information. - --------------------------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. NOTE: Third Party Rights 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. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. 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 =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 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 iQCVAwUBQ26rUSh9+71yA2DNAQJs/AQAnUR4OR8YfNbrI5w9R8MCLStw0225Mw/I 6yCO0UT1Bz51Ks3La1VSoPspFpb70rhsDWJvrIr11FPYQ9dX0ehzORrrGAJC3S7c 8jAOuYPXytTrGhY7+G93d3SlLTM0xvKPcLG1/8EbAxXJaaqW4pLbyws/x8oQTFpS rxnnEC5n7WM= =56Yw -----END PGP SIGNATURE-----