Quoting OpenSSL security advisory:

  http://openssl.org/news/secadv_20101202.txt

  A flaw has been found in the OpenSSL SSL/TLS server code where an old bug
  workaround allows malicous clients to modify the stored session cache
  ciphersuite. In some cases the ciphersuite can be downgraded to a weaker one
  on subsequent connections.

Problem affects SSL/TLS server that enable workaround for old Netscape server SSL implementation bug - SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG.  An attacker able to sniff session identifier (sent in plain during the SSL handshake) could use this flaw to force change of the cipher suite in stored session.  Client, that later resumes that session, may start using different (weaker) cipher suite chosen by attacker.

OpenSSL upstream version enable SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG when SSL_OP_ALL option is set (it's common to set this option in applications using OpenSSL).  However, OpenSSL versions in Red Hat Enterprise Linux 5 and 6 have SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG excluded from SSL_OP_ALL (the change was done in response to bug #175779).  Applications can enable Netscape bug workaround on those versions explicitly.

OpenSSL versions prior to 0.9.8j allowed attacker to change stored session cipher quite to arbitrary cipher suite supported by OpenSSL.  Version 0.9.8j corrected this issue to only allow changing cipher suite to those server is configured to use:
  http://cvs.openssl.org/chngview?cn=17489

In both cases, client must accept cipher suite change on resume for the downgrade attack to succeed.

Issue was addressed upstream in 0.9.8q and 1.0.0c by completely disabling this obsolete bug workaround:
  http://cvs.openssl.org/chngview?cn=20131