{"items":[{"id":"NVI-00010689","kind":"vulnerability","title":"PyJWT: HS256/384/512 verify accepts empty HMAC key via oct JWK (PyJWK/PyJWKClient) enabling token forgery","revision":1,"unknowns":["Customer inventory, deployment, reachability and exploitation have not been inspected."],"lifecycle":"active","identifiers":["GHSA-pxh4-856f-4h89"],"plain_summary":"GitHub lists this reviewed advisory for pyjwt. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.","review_status":"source_listed","control_topics":[],"public_actions":[{"summary":"Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.","source_ids":["sr-a8149309f1b530427cd667d8b40551dd"],"action_type":"investigate","limitations":"Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system.","current_supported_target":null}],"schema_version":"1.1.0","source_metrics":[{"kind":"CVSS","as_of":"2026-10-22T15:48:05.000Z","value":"7.4 high","meaning":"GitHub source severity; exploitability and local consequence require separate evidence.","source_id":"sr-a8149309f1b530427cd667d8b40551dd"}],"why_it_matters":"Published affected context helps an owner decide what evidence to gather. This report has not examined your application.","related_sources":[{"id":"sr-a8149309f1b530427cd667d8b40551dd","url":"https://github.com/advisories/GHSA-pxh4-856f-4h89","basis":"vendor_advisory","notes":"GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.","title":"GHSA-pxh4-856f-4h89","publisher":"GitHub Advisory Database","observed_at":"2026-10-31T22:07:30.906Z"}],"affected_context":[{"certainty":"source_listed","source_ids":["sr-a8149309f1b530427cd667d8b40551dd"],"technology":"pyjwt","known_exclusions":[],"conditions_summary":"### Summary\n\n`HMACAlgorithm.from_jwk` accepts a symmetric (`kty=oct`) JWK whose `k` value is\nthe empty string and returns a zero-length key without raising. When a token is\nthen verified with that key object (a `PyJWK`, or a `PyJWK` resolved by\n`PyJWKSet` / `PyJWKClient`), the HMAC verifier computes\n`HMAC(key=b\"\", signing_input)` and accepts any token an attacker forged with the\nsame empty key. The attacker needs no secret knowledge: they reproduce the digest\nlocally with an empty key and set the token's `kid` to the empty-`k` JWK.\n\nThe empty-key rejection that `HMACAlgorithm.prepare_key` performs for\nstring/bytes secrets (added in 2.13.0) was never propagated to the sibling\n`from_jwk` code path, so the JWK/JWKS verification route stays exploitable. Under\ndefault decode options this path only emits an `InsecureKeyLengthWarning`, not an\nerror, so verification still succeeds. This is the same \"empty/nil HMAC key is\naccepted by verify\" defect the JWT ecosystem is currently closing library-side:\nfast-jwt CVE-2026-44351 (CVSS 9.1) and ruby-jwt CVE-2026-45363 both added a\nlibrary-side reject-empty-HMAC-key precondition.\n\n### Affected versions\n\n`PyJWT` (PyPI package `pyjwt`) `<= 2.13.0`, ","public_affected_ranges":["<= 2.13.0"]}],"null_published_at":"2026-10-31T22:27:12.375Z","source_updated_at":"2026-10-22T15:48:05.000Z","source_disclosed_at":"2026-10-22T15:48:04.000Z","is_synthetic_fixture":false,"null_last_reviewed_at":null,"public_change_summary":"First indexed by Null; source disclosure date is shown separately.","null_first_observed_at":"2026-10-31T22:07:30.906Z"}],"next_cursor":null,"snapshot_revision":"42594"}