Ubuntu Security Notice USN-740-1 – The MD5 algorithm is known not to be collision resistant. This update blacklists the proof of concept rogue certificate authority as discussed in http://www.win.tue.nl/hashclash/rogue-ca/.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/75815/USN-740-1.txt
Source: https://packetstormsecurity.com/files/75815/Ubuntu-Security-Notice-740-1.html