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Thread: UW-IMAP Netmailbox Name Parsing Buffer Overflow Vulnerability!

  1. #1
    In And Above Man Black Cluster's Avatar
    Join Date
    Feb 2005

    UW-IMAP Netmailbox Name Parsing Buffer Overflow Vulnerability!

    I've just got this through email .....

    UW-IMAP Netmailbox Name Parsing Buffer Overflow Vulnerability

    iDEFENSE Security Advisory 10.04.05
    October 4, 2005


    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:



    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];
      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.


    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.


    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


    iDEFENSE is unaware of any valid workarounds for this issue. Restrict
    untrusted users from the IMAP service until the vendor releases a


    "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:



    The vulnerability is in the c-client library, which is used by the IMAP

    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

    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


    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.


    09/15/2005 Initial vendor notification
    09/15/2005 Initial vendor response
    10/04/2005 Coordinated public disclosure


    infamous41md@hotpop.com is credited with discovering this vulnerability.

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    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.
    \"The only truly secure system is one that is powered off, cast in a block of concrete and sealed in a lead-lined room with armed guards - and even then I have my doubts\".....Spaf
    Everytime I learn a new thing, I discover how ignorant I am.- ... Black Cluster

  2. #2
    Join Date
    Apr 2003
    yeah, them DAWGS ... putting winky smilies in code! Who'd'a thunk!

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