The following security advisory is sent to the securiteam mailing list, and can
be found at the SecuriTeam web site: http://www.securiteam.com
- - promotion
The SecuriTeam alerts list - Free, Accurate, Independent.
Get your security news from a reliable source.
http://www.securiteam.com/mailinglist.html
- - - - - - - - -
Clearswift MAILsweeper Multiple Encoding/Compression Issues
------------------------------------------------------------------------
SUMMARY
The MAILsweeper product provides policy based, email content security
functionality. Part of this functionality allows the product to block
attachments based on the type of content (i.e. executable) or name of the
attachment.
Encoding and compression technology is now commonly used to make the
transfer of data by email more efficient. Due to this, it is essential
that a product such as MAILsweeper can detect and analyze the content
contained within, or at least "fail closed" if a positive identification
cannot be made.
However, MAILsweeper does not detect a number of common compression
formats (for which it is listed as compatible) and in certain
circumstances also fails to identify the name of file attachments when
they are encoded.
DETAILS
Vulnerable Systems:
* Clearswift MAILsweeper version 4.3.14 and prior
Immune Systems:
* Clearswift MAILsweeper version 4.3.15 or newer
Analysis:
The MAILsweeper attachment detection functionality works by recursively
analyzing the email message body for container constructs (such as MIME
and compressed archives etc.), decoding these and then comparing the
contents against a predefined policy.
The current product
<http://www.clearswift.com/products/msw/smtp/techspec.asp> spec sheet
lists that the product is compatible with "ARJ (including self-extracting
ARJ), GZip, RAR, TAR, PGP, LZH, LHA, CMP, ZIP (multiple variants), BinHex
and CAB, MIME, UUE, TNEF, and binary". This is a subset of the available
compression formats, but does cover the majority of those in common use.
For analysis purposes, a collection of the freely available compression
tools was assembled. A sample executable file was then added to each
container type and then these were passed through a MAILsweeper host
configured with the latest available patches (CS MAILsweeper 4.3 for SMTP
Hotfix 4.3.10 and Technology Update 1.4.10).
The results were as per the following table. Where version information for
the archive tool was available, it is listed:
Encoding Listed Detected Content Detected filenames
7ZIP (2.30) ........ No ........... No ................ No
ACE (2.2) .......... No ........... No ................ No
ARC (6.0) .......... No ........... No ................ No
ARJ (2.81) ......... Yes .......... Yes ............... Yes
BH ................. No ........... No ................ No
BASE64 ............. No ........... Yes ............... n/a
Binary ............. Yes .......... Yes ............... n/a
BINHEX ............. Yes .......... Yes ............... No
BZIP2 (1.0.2) ...... No ........... No ................ No
CAB ................ Yes .......... Yes ............... Yes
CMP ................ Yes .......... Not tested ........ Not tested
COMPRESS (4.2.4) ... No ........... Yes ............... Yes
GZIP (1.2.4) ....... Yes .......... Yes ............... Yes
HAP (3.05) ......... No ........... No ................ No
HPK (.78a0) ........ No ........... No ................ No
IMG ................ No ........... No ................ No
JAR ................ No ........... Yes ............... Yes
LHA (2.55e) ........ Yes .......... Yes ............... Yes
LZH (1.13c) ........ Yes .......... Yes ............... Yes
MIME ............... Yes .......... Yes ............... Yes
PAK (2.51) ......... No ........... No ................ No
PGP ................ Yes .......... Yes ............... Yes
RAR (2.90) ......... Yes .......... Yes ............... Yes
RAR (3.20) ......... Yes .......... No ................ No
RAWRITE (0.7) ...... No ........... No ................ No
DOS TAR (1.12) ..... Yes .......... As Undetermined ... As Undetermined
UNIX TAR (1.13) .... Yes .......... As Undetermined ... As Undetermined
TNEF ............... Yes .......... Yes ............... Yes
UUE ................ Yes .......... Yes ............... n/a
ZIP (2.04g) ........ Yes .......... Yes ............... Yes
ZIP (6.0d) ......... Yes .......... As Undetermined ... As Undetermined
ZOO (2.1) .......... No ........... No ................ No
Note: The CMP compression format was not analyzed as the tool appears to
be available on the Mac only and a suitable platform was not on hand
during testing.
In summary:
- There are a significant number of common formats that are not detected
by MAILsweeper (most notably the newer formats like 7ZIP and ACE).
- The TAR format that is listed as compatible doesn't seem to be
supported, producing a "corrupt" error for all versions tested.
- Several formats that are listed as compatible are actually version
dependent (RAR and ZIP).
- The BinHex (HQX) format is detected but it does not expose the
filenames contained within to scrutiny.
The MAILsweeper product works from a starting position of allowing all
content to pass, then specifically blocking undesirable attachments. By
virtue of the encoding formats not being detected, the container and the
contents are passed through the system without being analyzed.
Recommendations:
Clearswift have released the 4.3.15 Hotfix that corrects these issues.
This should be applied to all existing installations where appropriate.
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0928>
CAN-2003-0928,
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0929>
CAN-2003-0929 and
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0930>
CAN-2003-0930.
History:
Discovered: 07.08.03
Vendor notified verbally: 26.08.03
Vendor notified in writing: 05.11.03
Vendor patch released: 05.08.04
Document released: 13.08.04
As per the normal process for dealing with Clearswift, after months of
requesting a status update on these issues (without any response), the
patches for these vulnerabilities have been released without any
discussion or coordination with ourselves, and as is becoming the norm,
completely un-attributed.
ADDITIONAL INFORMATION
The information has been provided by <mailto:martin.oneal@corsaire.com>
Martin O'Neal.
The original article can be found at:
<http://www.corsaire.com/advisories/c030807-001.txt>
http://www.corsaire.com/advisories/c030807-001.txt
========================================
This bulletin is sent to members of the SecuriTeam mailing list.
To unsubscribe from the list, send mail with an empty subject line and body to:
list-unsubscribe@securiteam.com
In order to subscribe to the mailing list, simply forward this email to:
list-subscribe@securiteam.com
====================
====================
DISCLAIMER:
The information in this bulletin is provided "AS IS" without warranty of any
kind.
In no event shall we be liable for any damages whatsoever including direct,
indirect, incidental, consequential, loss of business profits or special
damages.
