The remote host is missing an update to thunderbird announced via advisory USN-1011-2.
Details follow:
USN-1011-1 fixed a vulnerability in Firefox. This update provides the corresponding update for Thunderbird.
Original advisory details:
Morten Krakvik discovered a heap-based buffer overflow in Firefox. If a user were tricked into navigating to a malicious site, an attacker could cause a denial of service or possibly execute arbitrary code as the user invoking the program.
Solution: The problem can be corrected by upgrading your system to the following package versions: