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Home » Security Advisories» NetBSD » Sendmail malformed multipart MIME messages

Sendmail malformed multipart MIME messages

Sendmail is vulnerable to a denial of service condition in the handling of malformed multipart MIME messages. This may allow a remote attacker to launch a denial of service attack against the sendmail host.

  • Vendor: NetBSD
  • Vendor ID: 2006-017
  • Date: June 14, 2006


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NetBSD Security Advisory 2006-017
=================================

Topic: Sendmail malformed multipart MIME messages

Version: NetBSD-current: source prior to May 30, 2006
NetBSD 3.0: affected
NetBSD 2.1: affected
NetBSD 2.0.*: affected
NetBSD 2.0: affected
pkgsrc: sendmail-8.13.6nb2 and earlier
sendmail-8.12.11nb2 and earlier

Severity: Denial of service

Fixed: NetBSD-current: May 30, 2006
NetBSD-3-0 branch: June 14, 2006
(3.0.1 will include the fix)
NetBSD-3 branch: June 14, 2006
NetBSD-2-1 branch: June 14, 2006
(2.1.1 will include the fix)
NetBSD-2-0 branch: June 14, 2006
(2.0.4 will include the fix)
NetBSD-2 branch: June 14, 2006
pkgsrc: sendmail-8.13.6nb3 corrects this issue
sendmail-8.12.11nb3 corrects this issue


Abstract
========

Sendmail is vulnerable to a denial of service condition in the handling of
malformed multipart MIME messages. This may allow a remote attacker
to launch a denial of service attack against the sendmail host.

This vulnerability has been assigned CVE reference CVE-2006-1173.


Technical Details
=================

A denial of service condition is triggered when sendmail processes a
malformed multipart MIME message. The message can cause the sendmail
process to exhaust its available per-process stack space and abort.
The sendmail server process is not impacted by the abnormal
termination of the child process handling the malformed mail, and will
continue to function. As such your MTA will continue processing mail.

However, an attacker can still cause a number of issues by repeatedly
triggering this vulnerability:

- By sending multiple malformed MIME messages an attacker may be
able to consume disk space with core dump files.
- Any malformed MIME messages will remain in the sendmail queue and
cause queue runs to abort. This may impact the delivery of other
messages in the queue.

Solutions and Workarounds
=========================

On NetBSD 2.0 and later, sendmail by default is bound to localhost
(127.0.0.0, ::1) only, and as such is not externally reachable. Only
hosts on which sendmail has been configured for external mail
reception are externally exploitable, although hosts running sendmail
for local delivery can still be reached by local users.

It is recommended that all users of affected versions update their
sendmail to include the fix.

The following instructions describe how to upgrade your sendmail
binaries by updating your source tree and rebuilding and
installing a new version of sendmail.

* NetBSD-current:

In response to this and previous issues, Sendmail was removed
entirely from the NetBSD base system on 2006-05-30. The
default MTA has been switched to Postfix. These changes will
be included in NetBSD 4.0 and later releases, and will affect
current users updating their systems and new snapshot installs
built past this date.

The decision to switch default MTA for 4.0 had already been
taken after NetBSD-SA2006-010, however this most recent issue
prompted the removal of sendmail prior to branching for the
4.0 release, in order to minimise the risk and maintenance
burden for any future sendmail issues.

Users of NetBSD-current will need to migrate their mail
configurations, either to using postfix in the base system, or
to a fixed sendmail (or one of several other MTAs) available
via pkgsrc. The pkgsrc sendmail has more enabled and optional
features than were or would ever be available in the base
system sendmail, and it is likely that many sendmail sites
were already using pkgsrc sendmail for this reason.

As sendmail was removed from the base distribution before the
fixes for this issue could be applied, it is recommended that
users running NetBSD-current from before 2006-05-30 should
perform a full release build and update their systems. These
users should should ensure that the obsolete and vulnerable
sendmail binaries are removed from their systems when
updating, via the postinstall utility.

For more information on how to do this, see:
http://www.netbsd.org/Documentation/current/

* NetBSD 3.*:

Systems running NetBSD 3.* sources dated from before
2006-06-14 should be upgraded from NetBSD 3.* sources dated
2006-06-15 or later.

The following files need to be updated from the
netbsd-3 or netbsd-3-0 CVS branch:
gnu/dist/sendmail/sendmail/deliver.c
gnu/dist/sendmail/sendmail/mime.c
gnu/dist/sendmail/sendmail/sendmail.h
gnu/dist/sendmail/sendmail/version.c

To update from CVS, re-build, and re-install sendmail:

# cd src
# cvs update -d -P -r gnu/dist/sendmail
# cd gnu/usr.sbin/sendmail
# make USETOOLS=no cleandir dependall
# make USETOOLS=no install

* NetBSD 2.*:

Systems running NetBSD 2.* sources dated from before
2006-06-14 should be upgraded from NetBSD 2.* sources dated
2006-06-15 or later.

The following files need to be updated from the
netbsd-2, netbsd-2-0 or netbsd-2-1 CVS branch:
gnu/dist/sendmail/sendmail/deliver.c
gnu/dist/sendmail/sendmail/mime.c
gnu/dist/sendmail/sendmail/sendmail.h
gnu/dist/sendmail/sendmail/version.c

To update from CVS, re-build, and re-install sendmail:

# cd src
# cvs update -d -P -r gnu/dist/sendmail
# cd gnu/usr.sbin/sendmail
# make USETOOLS=no cleandir dependall
# make USETOOLS=no install



Thanks To
=========

CERT for notification and co-ordination of the issue.
Sendmail Consortium for supplying the patches to address the issue.
Frank Sheiness for finding the problem.

Revision History
================

2006-06-14 Initial release


More Information
================

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2006-017.txt.asc

Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/.


Copyright 2006, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2006-017.txt,v 1.6 2006/06/14 19:50:37 adrianp Exp $

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