A malformed packet to a Half-Life engine will cause a denial of service when a write to a read-only memory zone occurs. Both Windows and Linux releases are affected.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/33768/memHalfLife.txt
Source: https://packetstormsecurity.com/files/33768/memHalfLife.txt.html