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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2005.0772 -- iDEFENSE Security Advisory 10.04.05 UW-IMAP Netmailbox Name Parsing Buffer Overflow Vulnerability 5 October 2005 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: UW-IMAP Publisher: iDEFENSE Operating System: UNIX variants Impact: Execute Arbitrary Code/Commands Access: Existing Account CVE Names: CAN-2005-2933 Original Bulletin: http://www.idefense.com/application/poi/display?id=313 - --------------------------BEGIN INCLUDED TEXT-------------------- UW-IMAP Netmailbox Name Parsing Buffer Overflow Vulnerability iDEFENSE Security Advisory 10.04.05 www.idefense.com/application/poi/display?id=313&type=vulnerabilities October 4, 2005 I. BACKGROUND UW-IMAP is a popular free IMAP service for Linux and UNIX systems and is distributed with various Linux distributions. More information can be found at the vendor website: http://www.washington.edu/imap/ II. DESCRIPTION Remote exploitation of a buffer overflow vulnerability in the University of Washington's IMAP Server (UW-IMAP) allows attackers to execute arbitrary code. The vulnerability specifically exists due to insufficient bounds checking on user-supplied values. The mail_valid_net_parse_work() function in src/c-client/mail.c is responsible for obtaining and validating the specified mailbox name from user-supplied data. An error in the parsing of supplied mailbox names will continue to copy memory after a " character has been parsed until another " character is found as shown here: long mail_valid_net_parse_work (char *name,NETMBX *mb,char *service) { int i,j; #define MAILTMPLEN 1024 /* size of a temporary buffer */ char c,*s,*t,*v,tmp[MAILTMPLEN],arg[MAILTMPLEN]; ...snip... if (t - v) { /* any switches or port specification? */ 1] strncpy (t = tmp,v,j); /* copy it */ tmp[j] = '\0'; /* tie it off */ ... if (*t == '"') { /* quoted string? */ 2] for (v = arg,i = 0,++t; (c = *t++) != '"';) { /* Vulnerability */ /* quote next character */ if (c == '\\') c = *t++; arg[i++] = c; } If an attacker supplys only one " character, the function will continue to copy bytes to the new pointer, overflowing the stack buffer and resulting in arbitrary code execution. III. ANALYSIS Successful exploitation of the vulnerability will result in the execution of arbitrary code with permissions of the IMAP server. The impact of this vulnerability is slightly reduced due to the requirement of valid credentials, however IMAP servers commonly are used for free webmail systems and other services which may give untrusted users valid credentials. Networks that restrict IMAP service access to trusted users are at low risk. IV. DETECTION iDEFENSE has confirmed the existence of this vulnerability in Washington University imap-2004c1. The following vendors include susceptible UW-IMAP packages within their respective operating system distributions: * FreeBSD Project: FreeBSD 5.x * Gentoo Foundation Inc.: Gentoo 2005.x * Debian Project: Linux 3.x * Red Hat Linux, Inc.: Fedora Core 1, 2, and 3 * Mandrakesoft SA: Mandriva Linux 9.x * Novell Inc.: SuSE Linux 9.x V. WORKAROUND iDEFENSE is unaware of any valid workarounds for this issue. Restrict untrusted users from the IMAP service until the vendor releases a patch. VI. VENDOR RESPONSE "The fix is in the following patch to imap-????/src/c-client/mail.c: - ------------------------------Cut Here---------------------------------- *** mail.c 2005/03/17 00:12:22 1.6 - --- mail.c 2005/09/15 16:48:46 *************** *** 691,698 **** - --- 691,700 ---- if (c == '=') { /* parse switches which take arguments */ if (*t == '"') { /* quoted string? */ for (v = arg,i = 0,++t; (c = *t++) != '"';) { + if (!c) return NIL; /* unterminated string */ /* quote next character */ if (c == '\\') c = *t++; + if (!c) return NIL; /* can't quote NUL either */ arg[i++] = c; } c = *t++; /* remember delimiter for later */ - ------------------------------Cut Here---------------------------------- This fix is in UW release imap-2004g, which is available from as the current release version on: ftp://ftp.cac.washington.edu/mail/imap.tar.Z IMPACT ANALYSIS: The vulnerability is in the c-client library, which is used by the IMAP server. The main impact of a successful exploit in the IMAP server is that an authorized user can execute arbitrary code, including gaining shell access, on the server. The code is executed with the authorized user's userid. A successful exploit in the IMAP server does NOT allow root access. UW imapd has an optional facility for anonymous access; this feature must be enabled specifically by the site and is rarely-enabled. Due to a security check specific to anonymous IMAP access, anonymous IMAP users can NOT exploit this vulnerability. In the absence of data to the contrary, I believe that this vulnerability is LOW risk to servers which permit shell access to authorized users; and is of LOW-MODERATE risk (unauthorized shell access to authorized users) to other servers. The vulnerability impacts all applications which use the c-client library, even if these applications do not use IMAP. In the IMAP server and most MUAs, the application runs with the user's credentials which reduces the overall risk. If the application runs with other credentials (e.g., webmail systems), the vulnerability may be of higher risk." VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CAN-2005-2933 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 09/15/2005 Initial vendor notification 09/15/2005 Initial vendor response 10/04/2005 Coordinated public disclosure IX. CREDIT infamous41md@hotpop.com is credited with discovering this vulnerability. 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 iQCVAwUBQ0Nduih9+71yA2DNAQLSLgP/XKMxX40O/bbOcZLzOA3ubiHFClRW8TSV UhLzQf7QyWuqRAAYGSo+CehwhNGPng41Vh+mT422FkGBcL54282PtDwQ10TmBzZt Gl/HZRKW4NvygXsb/5XmPioOISDm1a1ZPAA6ImR3ohiR/XS1P0nXuNSN21cJCaV5 AOC1e8nqnFQ= =hZtl -----END PGP SIGNATURE-----