Patch Forecast
Amber warning
Patch this week.

CVE-2026-101918 · GHSA-42vr-xj54-vc7v

PyJWT: Unauthenticated RecursionError DoS in pre-verification payload parse (PyJWKClient.get_signing_key_from_jwt / verify_signature=False)

Risk score
66/100
CVSS
7.5 v3.1
Exploit chance (30 days)
0.4%
Published
28 Sep 2026

Open in the live forecast Today's forecast

What to know

What it is
PyJWT is a Python implementation of JSON Web Token standards. From 2.0.0a1 until 2.15.0, PyJWT PyJWKClient.get_signing_key_from_jwt is affected because payload parser catches ValueError but not RecursionError. This occurs when an attacker-controlled recursively nested payload reaches json.loads. As a result, documente…
Affected
PyJWT (pip) >= 2.0.0a1, <= 2.14.0
Fix
Upgrade PyJWT to 2.15.0 or later.
Exploitation
Public proof of concept

Story map

Story map: PyJWTTHE FLAWSTHE FIXCVE-2026-101918UnauthenticatedRecursionError DoS inpre-verification payload parse…CVSS 7.5 · EPSS 0%CVE-2026-102268Asymmetric-PEM detectionbypass:whitespace/line-ending-mutat…CVSS 9.1 · EPSS 0%CVE-2026-102266PyJWK accepts empty HMACkeys, bypassing PyJWT'sempty-key validationCVSS 9.1 · EPSS 0%CVE-2026-101917PyJWT: PyJWKClient stillamplifies unauthenticatedJWKS fetches on unknown kid…CVSS 7.5 · EPSS 0%Upgrade PyJWT2.15.0 · 2.14.0or later on your release lineWho is exposedPyJWT (pip) <= 2.13.0AMBER · PATCH THIS WEEKPyJWTPyJWT is a Pythonimplementation of JSON WebToken standards. Prior to 2.14.0,is_pem_format in jwt/utils.pyis affected becauseis_pem_format does notrecognize every PEM…Where it standsPublic proof of conceptCONNECTS TOSame weaknessCWE-248 (CWE-248)63 other warnings in 30 days →Same productEarlier PyJWT warnings10 in the last 90 days →
Story map: the flaws, the fix, how it unfolded and what it connects to. Boxes link to the record or article.

At a glance

PyJWT: Amber, patch this week. PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, is_pem_format in jwt/utils.py is affected because is_pem_format does not recognize every PEM representation accepted by the cryptography loader. This occurs when an application mixes HMAC and asymmetric algorithms and supplies a mutated pub…

The flaws

  • CVE-2026-101918: Unauthenticated RecursionError DoS in pre-verification payload parse (PyJWKClient.get_signing_key_from_jwt / verify_signature=False) (CVSS 7.5 · EPSS 0%)
  • CVE-2026-102268: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion guard (CVSS 9.1 · EPSS 0%)
  • CVE-2026-102266: PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation (CVSS 9.1 · EPSS 0%)
  • CVE-2026-101917: PyJWT: PyJWKClient still amplifies unauthenticated JWKS fetches on unknown kid values (incomplete fix of CVE-2026-48524) (CVSS 7.5 · EPSS 0%)

The fix

Upgrade PyJWT: 2.15.0 · 2.14.0 or later on your release line

Who is exposed: PyJWT (pip) <= 2.13.0

Where it stands

  • Public proof of concept

Connects to

Why it is Amber

  • CVSS 7.5 high
  • Public exploit or proof of concept referenced
  • Remotely exploitable without logging in
  • On your watchlist: PyPI

Affected packages

PackageEcosystemVulnerableFixed in
PyJWTpip>= 2.0.0a1, <= 2.14.02.15.0

References

Original description

PyJWT is a Python implementation of JSON Web Token standards. From 2.0.0a1 until 2.15.0, PyJWT PyJWKClient.get_signing_key_from_jwt is affected because payload parser catches ValueError but not RecursionError. This occurs when an attacker-controlled recursively nested payload reaches json.loads. As a result, documented PyJWT exception handling does not contain the failure. Consequently, an unauthenticated request can raise an exception that may produce an HTTP 500 response. The advisory-defined affected implementation also includes jwt/api_jwt.py, verify_signature=False. This issue is fixed in version 2.15.0.

Last activity 28 Sep 2026. Patch Forecast updates every hour.