Preventing DROWN Attack
On March 1st 2016, OpenSSL released patches that disable the SSLv2 protocol by default, as well as removing SSLv2 EXPORT ciphers.
A cross-protocol attack was discovered that could lead to decryption of TLS sessions by using a server supporting SSLv2 and EXPORT cipher suites as a Bleichenbacher RSA padding oracle. Note that traffic between clients and non-vulnerable servers can be decrypted provided another server supporting SSLv2 and EXPORT ciphers (even with a different protocol such as SMTP, IMAP or POP) shares the RSA keys of the non-vulnerable server. This vulnerability is known as DROWN.
The vulnerability is referred by CVE as CVE-2016-0800.
Dell SonicWALL customers are encouraged to enable the following IPS signature to detect and block SSLv2 traffic:
- 5160 SSLv2.0 Client Hello