The official MonsterInsights Pro update distribution bucket (monster-insights.s3.amazonaws.com) was compromised. Both the current release (10.2.2) and the version MonsterInsights rolled back to (10.2.0) contain a malicious file, class-system-check.php. Three distinct variants were observed on 2026-06-11, all sharing the same AES-256-GCM key, confirming a single threat actor. The attacker retains write access to the S3 bucket and has been actively iterating on the payload throughout the day.
Weakness
The product contains functionality that is not documented, not part of the specification, and not accessible through an interface or command sequence that is obvious to the product’s users or administrators.