[Full-disclosure] iDEFENSE Security Advisory 10.04.05: UW-IMAP Netmailbox Name Parsing Buffer Overflow Vulnerability

2005-10-05T00:00:00
ID SECURITYVULNS:DOC:9867
Type securityvulns
Reporter Securityvulns
Modified 2005-10-05T00:00:00

Description

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

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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.


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