-----BEGIN PGP SIGNED MESSAGE-----
AUSCERT External Security Bulletin Redistribution
ESB-2005.0015 -- Exim security advisory
Two Exim vulnerabilities - SPA authentication and IPv6 address parsing
7 January 2005
AusCERT Security Bulletin Summary
Product: Exim 4.43 and prior
Operating System: UNIX variants
Impact: Execute Arbitrary Code/Commands
CVE Names: CAN-2005-0021 CAN-2005-0022
- --------------------------BEGIN INCLUDED TEXT--------------------
Two relatively minor (IMHO) security issues in Exim were raised over the
Christmas break. The patches below address them for the 4.43 release. The same
patches will probably easily retrofit onto quite a number of prior releases. I
have also put these fixes into the current source, and made a new snapshot for
In addition to the security patches, this snapshot contains some bug fixes and
tidies that were reported by testers of the previous snapshot.
Discussion of security issues
1. The function host_aton() can overflow a buffer if it is presented with an
illegal IPv6 address that has more than 8 components. The input to this
function is supposed to be checked; the report said that an unchecked value
could be passed via the command line (without specifying which command line
option, annoyingly). I found one such case, which was a call do a dnsdb
lookup for a PTR record, as part of testing expansions using -be. The first
patch below fixes this - as it happens, this change had already been made to
the current source.
The report stated that Exim was running as "exim" when the problem occurred:
with -be, Exim runs as the calling user. Therefore, either the report was
wrong, or there is another case that I could not find. However, if there is
another case, it will now be covered by the second patch below, which puts a
test into the host_aton() function itself. (This should, of course, have
been there all the time, as a bit of defensive programming, but hey, I'm
only human. :-)
2. The second report described a buffer overflow in the function
spa_base64_to_bits(), which is part of the code for SPA authentication. This
code originated in the Samba project. The overflow can be exploited only if
you are using SPA authentication. The remaining patches below fix this
problem by adding a buffer length parameter to the problem function. I have
tested that SPA authentication still works, but I don't have the tools to
test that an attempt to exploit the overflow is now detected.
Philip Hazel University of Cambridge Computing Service,
ph10@xxxxxxxxxxxxx Cambridge, England. Phone: +44 1223 334714.
- --------------------------END INCLUDED TEXT--------------------
You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to firstname.lastname@example.org
and we will forward your request to the appropriate person.
NOTE: Third Party Rights
This security bulletin is provided as a service to AusCERT's members. As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.
NOTE: This is only the original release of the security bulletin. It may
not be updated when updates to the original are made. If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.
Contact information for the authors of the original document is included
in the Security Bulletin above. If you have any questions or need further
information, please contact them directly.
Previous advisories and external security bulletins can be retrieved from:
If you believe that your computer system has been compromised or attacked in
any way, we encourage you to let us know by completing the secure National IT
Incident Reporting Form at:
Australian Computer Emergency Response Team
The University of Queensland
Internet Email: email@example.com
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for member emergencies only.
-----BEGIN PGP SIGNATURE-----
-----END PGP SIGNATURE-----