HISTFILE Unset to Hide Command History
This rule detects attempts to unset the HISTFILE environment variable over a TCP connection to port 22 (SSH). Unsetting HISTFILE is a common technique used by attackers to prevent their commands from being recorded in the shell history, thereby evading detection and forensic analysis. The rule specifically looks for the string "unset HISTFILE" case-insensitively within the TCP stream.
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