WebAuthn assertion accepted for an invalid account or ceremony context
The relying party accepts a passkey assertion without the required account, challenge, signature, origin, or verification binding.
Candidate CWE: CWE-287 · CWE-347
Test hypothesis#
Start from a working local WebAuthn ceremony. Compare one consumed assertion, one invalid signature, and a validly signed fixture violating one server-side policy. For username-first login, check credential ownership; for discoverable login, check that the user handle and credential resolve to the same account.
Evidence required#
Expected relying-party policy, credential owner, altered validation condition, server acceptance, and resulting protected identity. Identify the verifier check that failed; editing signed bytes alone does not isolate semantic validation.
Rule out false positives#
Valid passwordless login to the credential owner, supported related origins, no attestation requirement, or a zero/non-increasing counter by itself does not prove bypass or cloning.
Playbook and command references#
- MFA and passkeys: enrollment, proof, replacement, and recovery — Follow each authenticator from account binding to removal, and validate WebAuthn assertions without mistaking client UI or counter behavior for a security guarantee.
- Authentication, recovery, federation, and session lifecycle — Test registration, recovery, identity changes, invitations, SSO enforcement, and deprovisioning as one account state machine.
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.