SA21 : Security Vulnerability with Netscape SSLv3: Cipher Forcing

1101

03 March 2020

21 August 2006

CLOSED

HIGH

SUMMARY

 

Significant when the ProxySG is used as an HTTPS reverse proxy to offload web traffic.

ISSUES

 

Netscape's SSLv3 implementation had an issue where if an SSLv3 connection is initially established, the first available cipher is used. If a session is resumed, a different cipher may be chosen if it appears in the passed cipher list before the session's current cipher. This is a bug that can be used to change ciphers on the server. OpenSSL contains this bug if the SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG option is enabled during runtime. This option was introduced for compatibility reasons. The problem arises when different applications using OpenSSL?'s libssl library enable all compatibility options including SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG, thus enabling the bug.