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fetchmail-SA-2005-01: security announcement

Topic:    remote code injection vulnerability in fetchmail

Author:    Matthias Andree
Version:  1.02
Announced:  2005-07-21
Type:    buffer overrun/stack corruption/code injection
Impact:    account or system compromise possible through malicious
    or compromised POP3 servers
Danger:    high: in sensitive configurations, a full system
    compromise is possible
    (for 6.2.5.1: denial of service for the whole fetchmail
    system is possible)
CVE Name:  CAN-2005-2335
URL:    http://fetchmail.berlios.de/fetchmail-SA-2005-01.txt
    http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=212762
    http://www.vuxml.org/freebsd/3497d7be-2fef-45f4-8162-9063751b573a.html
    http://www.vuxml.org/freebsd/3f4ac724-fa8b-11d9-afcf-0060084a00e5.html
    http://www.freebsd.org/cgi/query-pr.cgi?pr=83805
    http://www.heise.de/security/news/meldung/62070
Thanks:    Edward J. Shornock (located the bug in UIDL code)
    Miloslav Trmac (pointed out 6.2.5.1 was faulty)
    Ludwig Nussel (provided minimal correct fix)

Affects:  fetchmail version 6.2.5.1 (denial of service)
    fetchmail version 6.2.5 (code injection)
    fetchmail version 6.2.0 (code injection)
    (other versions have not been checked)

Not affected:  fetchmail 6.2.5.2
    fetchmail 6.2.6-pre7
    fetchmail 6.3.0      (not released yet)

    Older versions may not have THIS bug, but had been found
    to contain other security-relevant bugs.

Corrected:  2005-07-22 01:37 UTC (SVN) - committed bugfix (r4157)
    2005-07-22                   fetchmail-patch-6.2.5.2 released
    2005-07-23                   fetchmail-6.2.5.2 tarball released

0. Release history

2005-07-20  1.00 - Initial announcement
2005-07-22  1.01 - Withdrew 6.2.5.1 and 6.2.6-pre5, the fix was buggy
           and susceptible to denial of service through
           single-byte read from 0 when either a Message-ID:
           header was empty (in violation of RFC-822/2822)
           or the UIDL response did not contain an UID (in
           violation of RFC-1939).
         - Add Credits.
         - Add 6.2.5.1 failure details to sections 2 and 3
         - Revise section 5 and B.
2005-07-26  1.02 - Revise section 0.
         - Add FreeBSD VuXML URL for 6.2.5.1.
         - Add heise security URL.
         - Mention release of 6.2.5.2 tarball.

1. Background

fetchmail is a software package to retrieve mail from remote POP2, POP3,
IMAP, ETRN or ODMR servers and forward it to local SMTP, LMTP servers or
message delivery agents.

2. Problem description

The POP3 code in fetchmail-6.2.5 and older that deals with UIDs (from
the UIDL) reads the responses returned by the POP3 server into
fixed-size buffers allocated on the stack, without limiting the input
length to the buffer size. A compromised or malicious POP3 server can
thus overrun fetchmail's stack.  This affects POP3 and all of its
variants, for instance but not limited to APOP.

In fetchmail-6.2.5.1, the attempted fix prevented code injection via
POP3 UIDL, but introduced two possible NULL dereferences that can be
exploited to mount a denial of service attack.

3. Impact

In fetchmail-6.2.5 and older, very long UIDs can cause fetchmail to
crash, or potentially make it execute code placed on the stack. In some
configurations, fetchmail is run by the root user to download mail for
multiple accounts.

In fetchmail-6.2.5.1, a server that responds with UID lines containing
only the article number but no UID (in violation of RFC-1939), or a
message without Message-ID when no UIDL support is available, can crash
fetchmail.

4. Workaround

No reasonable workaround can be offered at this time.

5. Solution

Upgrade your fetchmail package to version 6.2.5.2.

You can either download a complete tarball of fetchmail-6.2.5.2.tar.gz,
or you can download a patch against fetchmail-6.2.5 if you already have
the 6.2.5 tarball. Either is available from:

<http://developer.berlios.de/project/showfiles.php?group_id=1824>

To use the patch:

  1. download fetchmail-6.2.5.tar.gz (or retrieve the version you already
     had downloaded) and fetchmail-patch-6.2.5.2.tar.gz
  2. unpack the tarball: gunzip -c fetchmail-6.2.5.tar.gz | tar xf -
  3. unpack the patch: gunzip fetchmail-patch-6.2.5.2.gz
  4. apply the patch: cd fetchmail-6.2.5 ; patch -p1 <../fetchmail-patch-6.2.5.2
  5. now configure and build as usual - detailed instructions in the file
     named "INSTALL".

A. References

fetchmail home page: <http://fetchmail.berlios.de/>

B. Copyright, License and Warranty

(C) Copyright 2005 by Matthias Andree, <matthias.andree@gmx.de>.
Some rights reserved.

This work is licensed under the Creative Commons
Attribution-NonCommercial-NoDerivs German License. To view a copy of
this license, visit http://creativecommons.org/licenses/by-nc-nd/2.0/de/
or send a letter to Creative Commons; 559 Nathan Abbott Way;
Stanford, California 94305; USA.

THIS WORK IS PROVIDED FREE OF CHARGE AND WITHOUT ANY WARRANTIES.
Use the information herein at your own risk.

END OF fetchmail-SA-2005-01.txt
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