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OpenSSL SSL 2.0 Rollback
------------------------------------------------------------------------
SUMMARY
A vulnerability has been found in all previously released versions of
OpenSSL (all versions up to 0.9.7h and 0.9.8a). Versions 0.9.7h and 0.9.8a
have been released to address the issue. The vulnerability potentially
affects applications that use the SSL/TLS server implementation provided
by OpenSSL.
DETAILS
Applications that use the option SSL_OP_MSIE_SSLV2_RSA_PADDING are
affected by the OpenSSL Roolback vulnerability. This option is implied by
use of SSL_OP_ALL, which is intended to work around various bugs in
third-party software that might prevent interoperability. The
SSL_OP_MSIE_SSLV2_RSA_PADDING option disables a verification step in the
SSL 2.0 server supposed to prevent active protocol-version rollback
attacks. With this verification step disabled, an attacker acting as a
"man in the middle" can force a client and a server to negotiate the SSL
2.0 protocol even if these parties both support SSL 3.0 or TLS 1.0. The
SSL 2.0 protocol is known to have severe cryptographic weaknesses and is
supported as a fallback only.
Applications using neither SSL_OP_MSIE_SSLV2_RSA_PADDING nor SSL_OP_ALL
are not affected. Also, applications that disable
use of SSL 2.0 are not affected.
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2969>
CAN-2005-2969
Recommendations:
There are multiple ways to avoid this vulnerability. Any one of the
following measures is sufficient.
1. Disable SSL 2.0 in the OpenSSL-based application.
The vulnerability occurs only if the old protocol version SSL 2.0 is
enabled both in an OpenSSL server and in any of the clients (OpenSSL-based
or not) connecting to it. Thus, if you have disabled SSL 2.0, the
vulnerability does not apply to you. Generally, it is strongly recommended
to disable the SSL 2.0 protocol because of its known weaknesses.
2. Upgrade the OpenSSL server software.
The vulnerability is resolved in the following versions of OpenSSL:
- in the 0.9.7 branch, version 0.9.7h (or later);
- in the 0.9.8 branch, version 0.9.8a (or later).
OpenSSL 0.9.8a and OpenSSL 0.9.7h are 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):
* http://www.openssl.org/source/
* ftp://ftp.openssl.org/source/
The distribution file names are:
* openssl-0.9.8a.tar.gz
MD5 checksum: 1d16c727c10185e4d694f87f5e424ee1
SHA1 checksum: 2aaba0f728179370fb3e86b43209205bc6c06a3a
* openssl-0.9.7h.tar.gz
MD5 checksum: 8dc90a113eb8925795071fbe52b2932c
SHA1 checksum: 9fe535fce89af967b29c4727dedd25f2b4cc2f0d
The checksums were calculated using the following commands:
openssl md5 openssl-0.9*.tar.gz
openssl sha1 openssl-0.9*.tar.gz
If this version upgrade is not an option at the present time,
alternatively the following patch may be applied to the OpenSSL source
code to resolve the problem. The patch is compatible with the 0.9.6,
0.9.7, and 0.9.8 branches of OpenSSL.:
<http://www.openssl.org/news/patch-CAN-2005-2969.txt>
http://www.openssl.org/news/patch-CAN-2005-2969.txt
Whether you choose to upgrade to a new version or to apply the patch, make
sure to recompile any applications statically linked to OpenSSL libraries
if these applications use the OpenSSL SSL/TLS server implementation.
Acknowledgement:
The OpenSSL team thank Yutaka Oiwa of the Research Center for Information
Security, National Institute of Advanced Industrial Science and Technology
(AIST), Japan, for alerting us about this problem.
ADDITIONAL INFORMATION
The information has been provided by <mailto:mark@openssl.org> Mark J
Cox.
The original article can be found at:
<http://www.openssl.org/news/secadv_20051011.txt>
http://www.openssl.org/news/secadv_20051011.txt
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