PyJWT: Non-canonical signature segments enable raw-token revocation bypass — GHSA-HXM8-2XGR-2P9M

Summary

## Summary PyJWT 2.13.0 accepts compact JWS signature segments containing characters that are not in the Base64URL alphabet. Appending `!!!!` to a valid signature does not change the decoded signature bytes or authenticated claims, but it changes the serialized token and its SHA-256 hash. An application that indexes logout or revocation state by the raw token therefore rejects the logged-out token and accepts its…

Timeline

Published by source

2026-09-29

Risk context

• Reported severity or threat level: medium.
• Reported CVSS score: 4.8 out of 10.
• Reported EPSS value: 0.00198.
• 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):

• Review exposure and plan remediation based on risk and environment.
• 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-HXM8-2XGR-2P9M

Source

GitHub

Vendor

GitHub

Published by source

2026-09-29

Last source activity

2026-09-29

Additional identifiers

CVE-2026-102269

Curated by

hlukh.ch

Related advisories and connections

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