Question

A detection engineer is writing a YARA-L rule to detect a specific attack: a single process both writes a file to a startup directory AND, within the same event, is flagged by the endpoint agent as low-reputation. Both conditions are fully described by fields within one individual process/file UDM event. The engineer's first draft uses two placeholder variables ($e1 and $e2) joined on principal.hostname with a 5-minute match window. Peer review flags this as unnecessarily complex. What is the most appropriate correction?

Accepted Answer

Rewrite the rule as a single-event rule referencing one event variable, since all conditions apply to the same UDM record and no correlation across separate events is required.

Answer

Keep the multi-event structure but shorten the match window to 1 minute to reduce false positives from unrelated events.

Answer

Keep the two placeholders but change the join key from principal.hostname to principal.process.pid for tighter correlation.

Answer

Convert the rule to a multi-event rule with an outcome section that counts distinct file writes above a threshold.