Via the Steam Store:
An update has been released for Left 4 Dead 2.
- Fixed some potential remote code execution exploits. Reported via HackerOne.
- Updates to caption localization.
Left 4 Dead 2 update for August 21, 2018
View all patches · Build 3049377 · Last edited August 21, 2018 – 17:15:54 UTC by 
Wendy