Checking Debian Based OpenSSL/OpenSSH Keys Against The Blacklist

Recently there has been a serious security vulnerability with OpenSSL/SSH keys generated on Debian based systems. Since I use Ubuntu at home I wanted to check to see if any of my keys needed to be regenerated. I wasn’t sure if they update automatically regenerated them for you or just checked the keys against the blacklist. Since there are many applications that generate keys I thought it would be best to manually verify them. For more insight into the problem I’ve quoted the Metasploit article found here.

All SSL and SSH keys generated on Debian-based systems (Ubuntu, Kubuntu, etc) between September 2006 and May 13th, 2008 may be affected. In the case of SSL keys, all generated certificates will be need to recreated and sent off to the Certificate Authority to sign. Any Certificate Authority keys generated on a Debian-based system will need be regenerated and revoked. All system administrators that allow users to access their servers with SSH and public key authentication need to audit those keys to see if any of them were created on a vulnerabile system. Any tools that relied on OpenSSL’s PRNG to secure the data they transferred may be vulnerable to an offline attack. Any SSH server that uses a host key generated by a flawed system is subject to traffic decryption and a man-in-the-middle attack would be invisible to the users. This flaw is ugly because even systems that do not use the Debian software need to be audited in case any key is being used that was created on a Debian system. The Debian and Ubuntu projects have released a set of tools for identifying vulnerable keys. You can find these listed in the references section below.

To check if your SSH keys are affected by the issue you can simply run sudo ssh-vulnkey -a. This will check all keys on your system in standard locations. What about the other applications that have keys? Well lucky for me (and you) there is a article on Debian’s wiki with a list of applications and the steps needed to generate new keys. Additional information can be found here and here.