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TUCoPS :: Web :: General :: bt1628.txt

OpenSSL Denial of Service in ASN.1 parsing





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OpenSSL Security Advisory [4 November 2003]

Denial of Service in ASN.1 parsing
==================================

Previously, OpenSSL 0.9.6k was released on the 30 September 2003 to
address various ASN.1 issues.  The issues were found using a test
suite from NISCC (www.niscc.gov.uk) and fixed by Dr Stephen Henson
(steve@openssl.org) of the OpenSSL core team.

Subsequent to that release, Novell Inc. carried out further testing
using the NISCC suite.  They discovered that there was a denial of
service vulnerability in OpenSSL version 0.9.6k when running on a
Windows platform.

A bug in OpenSSL 0.9.6 would cause certain ASN.1 sequences to trigger
a large recursion.  On platforms such as Windows this large recursion
cannot be handled correctly and so the bug causes OpenSSL to crash.  A
remote attacker could exploit this flaw if they can send arbitrary
ASN.1 sequences which would cause OpenSSL to crash.  This could be
performed for example by sending a client certificate to a SSL/TLS
enabled server which is configured to accept them.

We do not believe this issue could be exploited further than a Denial
of Service attack.  

Patches for this issue have been created by Dr Stephen Henson
(steve@openssl.org) of the OpenSSL core team.

Who is affected?
- ----------------

OpenSSL 0.9.6k is affected by the bug, but the denial of service does
not affect all platforms.  This issue does not affect OpenSSL 0.9.7.
Currently only OpenSSL running on Windows platforms is known to crash.

Recommendations
- ---------------

Upgrade to OpenSSL 0.9.6l or 0.9.7c.  Recompile any OpenSSL
applications statically linked to OpenSSL libraries.

OpenSSL 0.9.6l is available for download via HTTP and FTP from the
following master locations (you can find the various FTP mirrors under
http://www.openssl.org/source/mirror.html):

    o http://www.openssl.org/source/
    o ftp://ftp.openssl.org/source/

The distribution file name is:

    o openssl-0.9.6l.tar.gz [normal]
      MD5 checksum: 843a65ddc56634f0e30a4f9474bb5b27
    o openssl-engine-0.9.6l.tar.gz [engine]
      MD5 checksum: dd372198cdf31667f2cb29cd76fbda1c

The checksums were calculated using the following command:

    openssl md5 < openssl-0.9.6l.tar.gz
    openssl md5 < openssl-engine-0.9.6l.tar.gz

References
- ----------

The Common Vulnerabilities and Exposures project (cve.mitre.org) has
assigned the name CAN-2003-0851 to this issue.

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0851

URL for this Security Advisory:
http://www.openssl.org/news/secadv_20031104.txt
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