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Security advisory 20031002
- ----------------------------------------------------------------------
     Product: openssl
  Issue date: 2003/10/02
Last updated: 2003/10/02
======================================================================



OpenSSL remote vulnerability
============================

Mr. Hornik discovered remote vulnerability in OpenSSL package provided
by  RedHat.  Because  of  nature of this bug some other vendors can be
vulnerable  too.  This  vulnerability  is inside SSLv2 server code and
allows  killing  remote process running OpenSSL library as SSL server,
resulting in DoS.

The  vulnerability is different from one found in SSLv2 OpenSSL server
announced on 2002/07/30.


Vulnerability
- -------------

By  constructing special SSLv2 CLIENT_MASTER_KEY message the following
execution path can be obtained - we are reffering to source lines from
openssl-0.9.6b-32.7.src.rpm from RH 7.3.

When:
i, negotated cipher is some export cipher, for example EXP-RC4-MD5
ii, length of the clear is increased for example by 64 (see below)

Then this execution path happens:
1, on ssl/s2_srvr.c:419 condition is_export && (s->s2->tmp.clear+i !=
   EVP_CIPHER_key_length(c)) becomes true because of i, and ii,
2, on ssl/s2_srvr.c:424 i is "fixed", but tmp.clear stays unchanged
3, on ssl/s2_srvr.c:450 because is_export is true integer variable i
   is increased by big enough value (ii,)
4, on ssl/s2_srvr.c:451 die causes abort of the process leading to DoS


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

Affected  are  all  RedHat  distributions up to version 8.0 including.
RedHat  published patch on 2003/09/30 silently without issuing warning
about  existence  of  vulnerability. RedHat announced the patch in its
advisory RHSA-2003:291-11.

openssl.org  sources  starting  with  version  0.9.6f and distribution
packages  based  on these versions are not vulnerable, because OpenSSL
starting  from  0.9.6f  are  avoiding  using die() call because of its
potential risk.


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

We  recommend  to  upgrade  openssl  package  to the version issued on
2003/09/30  and after in all RedHat distributions up to 8.0. Until the
new   version   will  be  installed  we  recommend  to  disable  SSLv2
functionality  whenever  it  is  possible.  (In  Apache  + mod_ssl for
example  it is enabled by default and it can be disabled, please refer
to mod_ssl documentation.)


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

OpenSSL project:
http://www.openssl.org/
OpenSSL vulnerability announced on 2002/07/30:
http://www.openssl.org/news/secadv_20020730.txt

This security advisory:
http://www.ebitech.sk/patrik/SA/SA-20031002.txt


Contact
- -------

Patrik Hornik
- --
Security Consultant

Email: patrik.hornik@ebitech.sk
Phone: +421 905 385 666
PGP KeyID: DFA5BC67

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