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AUSCERT External Security Bulletin Redistribution
ESB-2003.0760 -- UNIRAS Brief - 603/03
NISCC Vulnerability Advisory - 006489/SMIME
05 November 2003
AusCERT Security Bulletin Summary
Publisher: UNIRAS (UK Govt. CERT)
Impact: Denial of Service
Execute Arbitrary Code/Commands
Access Required: Remote
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NISCC Vulnerability Advisory - 006489/SMIME
Vulnerability Issues in Implementations of the S/MIME Protocol
Advisory Reference 006489/SMIME
Release DatE 4 November 2003
Last Revision 4 November 2003
What is affected?
The vulnerabilities described in this advisory affect the S/MIME
protocol, which is typically used to provide security services to
Many vendors include support for S/MIME in their products.
The severity of these vulnerabilities varies by vendor. In some cases,
they could allow an attacker to create a denial-of-service
condition. There are indications that it may be possible to execute
code as a result of a buffer overflow, but this has not been
During 2002 the University of Oulu Security Programming Group (OUSPG)
discovered a number of implementation specific vulnerabilities in the
Simple Network Management Protocol (SNMP). NISCC has performed and
commissioned further work to identify implementation specific
vulnerabilities in related protocols that are critical to the UK
Critical National Infrastructure. The S/MIME (secure multipurpose
Internet mail extensions), which provides services such as digital
signatures and encryption to e-mail, has been studied in this context.
NISCC has produced a test suite for S/MIME and has employed it to
validate a number of products from different vendors. The test results
have been confirmed, and the affected vendors have been contacted with
the test results. These vendors' product lines cover a great deal of
the existing critical information infrastructure worldwide and have
therefore been addressed as a priority. However, NISCC has
subsequently contacted other vendors whose products employ S/MIME and
provided them with tools with which to test their implementations.
S/MIME is a set of protocols intended to provide security services,
such as digital signatures and encryption, to e-mail. MIME
(multipurpose Internet mail extensions) allows binary objects and
attachments to be sent across an e-mail system; S/MIME specifies a
mechanism by which MIME attachments may be exchanged in a consistent
and secure fashion.
(Although principally used to provide secure e-mail, S/MIME objects
may, in theory, be passed by mechanisms other than e-mail. Such
mechanisms are beyond the scope of this advisory.)
S/MIME extends MIME by including the secure data in an attachment
encoded using ASN.1 (Abstract Syntax Notation One). If one of the
entities in an e-mail system knowingly or unknowingly send an
exceptional ASN.1 element that cannot be handled properly by another
party, the behaviour of the application receiving such an element is
unpredictable. A denial-of-service may result, or there may be an
opportunity for further exploitation. Both client and server software
may be affected in this way.
Vendor specific information will be released as it becomes available,
but information will only be released with vendors'
permission. Subscribers are advised to check the following URL
regularly for updates:
[Please note that revisions to this advisory will not be notified by
Please refer to the Vendor Information section of this advisory for
platform specific remediation.
A list of vendors affected by this vulnerability is not currently
available. Please visit the web site,
http://www.uniras.gov.uk/vuls/2003/006489/smime.htm, in order to check
The NISCC Vulnerability Management Team can be contacted as follows:
Please quote the advisory reference in the subject line.
Telephone +44 (0) 20 7821 1330 Ext 4511
Monday - Friday 08:30 - 17:00 hrs
Fax +44 (0) 20 7821 1686
Post Vulnerability Management Team
PO Box 832
We encourage those who wish to communicate via e-mail to make use of
our PGP key. This is available from
Please note that UK government protectively marked material should not
be sent to the e-mail address above.
If you wish to be added to our e-mail distribution list please e-mail
your request to email@example.com.
What is NISCC?
For further information regarding the UK National Infrastructure
Security Co-ordination Centre, please visit
Reference to any specific commercial product, process, or service by
trade name, trademark manufacturer, or otherwise, does not constitute
or imply its endorsement, recommendation, or favouring by NISCC. The
views and opinions of authors expressed within this notice shall not
be used for advertising or product endorsement purposes.
Neither shall NISCC accept responsibility for any errors or omissions
contained within this briefing notice. In particular, they shall not
be liable for any loss or damage whatsoever, arising from or in
connection with the usage of information contained within this notice.
(C) 2003 Crown Copyright
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