[IT-SecNots] [SECURITY] [DSA-2154-1] exim4 security update

[Stefan Fritsch <sf AT debian.org>]

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Debian Security Advisory DSA-2154-1                  security AT debian.org
http://www.debian.org/security/                           Stefan Fritsch
January 30, 2011                      http://www.debian.org/security/faq
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Package          : exim4
Vulnerability    : privilege escalation
Problem type     : local
CVE Id(s)        : CVE-2010-4345 CVE-2011-0017
Behaviour change : yes

A design flaw (CVE-2010-4345) in exim4 allowed the loal Debian-exim
user to obtain root privileges by specifying an alternate
configuration file using the -C option or by using the macro override
facility (-D option).  Unfortunately, fixing this vulnerability is not
possible without some changes in exim4's behvaviour. If you use the -C
or -D options or use the system filter facility, you should evaluate
the changes carefully and adjust your configuration accordingly. The
Debian default configuration is not affected by the changes.

The detailed list of changes is described in the NEWS.Debian file in
the packages. The relevant sections are also reproduced below.

In addition to that, missing error handling for the setuid/setgid
system calls allowed the Debian-exim user to cause root to append
log data to arbitrary files (CVE-2011-0017).

For the stable distribution (lenny), these problems have been fixed in
version 4.69-9+lenny3.

For the testing distribution (squeeze) and the unstable distribution
(sid), these problem have been fixed in version 4.72-4.

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at: http://www.debian.org/security/

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Excerpt from the NEWS.Debian file from the packages exim4-daemon-light
and exim4-daemon-heavy:

Exim versions up to and including 4.72 are vulnerable to
CVE-2010-4345. This is a privilege escalation issue that allows the
exim user to gain root privileges by specifying an alternate
configuration file using the -C option. The macro override facility
(-D) might also be misused for this purpose.

In reaction to this security vulnerability upstream has made a number
of user visible changes. This package includes these changes.

If exim is invoked with the -C or -D option the daemon will not regain
root privileges though re-execution. This is usually necessary for
local delivery, though. Therefore it is generally not possible anymore
to run an exim daemon with -D or -C options.

However this version of exim has been built with
TRUSTED_CONFIG_LIST=/etc/exim4/trusted_configs. TRUSTED_CONFIG_LIST
defines a list of configuration files which are trusted; if a config
file is owned by root and matches a pathname in the list, then it may
be invoked by the Exim build-time user without Exim relinquishing root
privileges.

As a hotfix to not break existing installations of mailscanner we have
also set WHITELIST_D_MACROS=OUTGOING. i.e. it is still possible to
start exim with -DOUTGOING while being able to do local deliveries.

If you previously were using -D switches you will need to change your
setup to use a separate configuration file. The ".include" mechanism
makes this easy.

The system filter is run as exim_user instead of root by default.  If
your setup requies root privileges when running the system filter you
will need to set the system_filter_user exim main configuration
option.
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Mailing list: debian-security-announce AT lists.debian.org

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