Last Updated: 2012-04-27 01:27:42 UTC
by Johannes Ullrich (Version: 1)
Oracles April "Critical Patch Update" listed a vulnerability in the TNS Listener services as one of the patched vulnerabilities. Sadly, it turns out that current versions of Oracle are not patched. Instead, the vulnerability will apparently only be fixed in future versions of the Oracle database. According to a statement from Oracle quoted by the discoverer of the vulnerability, the fix would have possible had stability issues for current versions of Oracle. 
The vulnerability was responsibly reported to Oracle back in 2008. Upon release of the April CPU, Joxean Koret, who originally found the vulnerability, came forward with additional details including a proof of concept exploit, fully expecting that a patch is now available.
So in short: We got an unpatched remote code execution vulnerability in all current versions of Oracle with proof of concept exploit code.
Joxean's details published after the CPU release also include some useful workarounds . Please refer to the post for details.