SMTP relay allows unauthenticated external delivery
An untrusted unauthenticated client can relay between external domains contrary to the server's relay policy.
Candidate CWE: CWE-441
Test hypothesis#
When mail delivery is explicitly covered, send one inert marked message from an owned sender domain to an owned external receiver through the tested relay. Use a source outside trusted networks and no inherited SMTP authentication.
Evidence required#
Source address, no-AUTH transcript, external envelope identities, queue response and receiver-confirmed delivery of the marker. Preserve the permitted submission comparison.
Rule out false positives#
Delivery to local domains, an allowlisted source, intended authenticated submission, RCPT acceptance without delivery, or a message routed through a different server.
Playbook and command references#
- DNS, TLS and email trust boundaries — Separate dangling records, transfer/recursion exposure, TLS identity and SMTP relay into controlled protocol tests.
Find the associated command snippets
Referenced by these target playbooks#
Report checklist#
- Capture the affected version, configuration, identities, and object ownership.
- Preserve a valid baseline and a negative control.
- Reproduce the forbidden data access, action, or state change on controlled fixtures.
- Explain the intended security rule and why the observed behavior violates it.
- State prerequisites, uncertainty, cleanup, and the smallest demonstrated impact.
Conditional ATT&CK mapping#
No direct ATT&CK mapping selected. Record the weakness and demonstrated impact without forcing an adversary-behavior classification. See the mapping guide.