Developer finds own security scanner missed half a critical CI vulnerability pattern

A developer maintaining mcpscan, an open-source static security scanner for GitHub Actions workflows, discovered that a newly shipped rule in version 0.14.0 only detected one of two known attack paths for a common CI vulnerability. The flaw involves workflow_run triggers, which always execute with full repository token privileges regardless of whether the originating workflow was launched by an untrusted fork pull request. Two distinct attack shapes exist: one where a workflow checks out attacker-controlled code via a commit hash, and another where it downloads and executes a build artifact produced by the untrusted run. The original rule only flagged artifact reuse cases and only when no permissions block was present, creating blind spots for direct checkout abuse and loosely scoped but still dangerous token configurations. The developer has since revised the rule to treat both attack shapes as independently reportable, decoupling the permissions check from the artifact reuse detection.