FYI 100% work for Lewd4Dead servers in LFD2 but might be obsolete for the game:
March 27, 2019 - L4D Team
An update has been released for Left 4 Dead 2. - Fixed a spectate command exploit that caused servers to hang. - Fixed lobby chat messages not appearing on Linux.
Apparent exact minimum command needed to have trigger buffer overflow:
spec_goto 0 0 274877923328.1 0 0
Someone wrote about it here but never expanded on the malform parameters bit which may still keep alternative spec_goto fixes relevent:
spec_goto: How to instantly crash any L4D2 server (and how Admins can patch it)
Keeping plugin installed regardless, ta.