CVE-2021-27216 — Exim 4 before 4.94.2 has Execution with Unnecessary Privileges

Matched remediation archetype

Race condition, TOCTOU, and lifecycle synchronization

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

• Map concurrent actors, shared state, lock boundaries, signals, callbacks, retries, and check-then-use sequences in the affected path.
• Determine whether untrusted users can influence timing, object names, filesystem state, or repeated state transitions.
• Identify clustered and multi-process behavior that repository-local tests may not represent.

Remediate safely

• Make the sensitive state transition atomic or protect it with a consistently ordered synchronization primitive.
• Perform authorization and invariant checks on the same authoritative object and transaction used for the operation.
• Use unique private resources, safe ownership transfer, and idempotent operations; add deterministic concurrency regression tests.