PyJWT: PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation — GHSA-9J54-FG26-WV3R

Summary

### Summary A service that verifies HS256 tokens using an empty oct JWK through PyJWK, including a PyJWK obtained from PyJWKSet, can therefore accept attacker-generated tokens as authenticated. PyJWT 2.13.0 rejects an empty HMAC key when it is supplied through the raw `str`/`bytes` key path, but accepts the same zero-length key when it is supplied as a symmetric `PyJWK`. An `oct` JWK containing an empty Base64URL…

Timeline

Published by source

2026-09-29

Risk context

• Reported severity or threat level: high.
• Reported CVSS score: 7.4 out of 10.
• Reported EPSS value: 0.00175.
• Review exposure for the affected product or family: pip: PyJWT.

Product

pip: PyJWT

What to do

General, cautious steps (verify details in the official source):

• Prioritize patching or mitigation immediately (treat as actively risky).
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source
• CVE Record
• NVD

Evidence and provenance

Canonical advisory ID

GHSA-9J54-FG26-WV3R

Source

GitHub

Vendor

GitHub

Published by source

2026-09-29

Last source activity

2026-09-29

Additional identifiers

CVE-2026-102266

Curated by

hlukh.ch

Related advisories and connections

These advisories are connected by shared CVE, product, vendor, source, or time signals.