Vulnerability · Published Sep 28, 2026 · Assigned by GitHub_M

CVE-2026-101918PyJWT: Unauthenticated RecursionError DoS in pre-verification payload parse (PyJWKClient.get_signing_key_from_jwt / verify_signature=False)

Medium 5.3

In plain English

A medium-severity security flaw in pyjwt from jpadilla. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.4%top 64.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	pyjwt	no fix listed	DEBIAN-CVE-2026-101918
Debian:13	pyjwt	no fix listed	DEBIAN-CVE-2026-101918
Debian:14	pyjwt	2.15.0-1	DEBIAN-CVE-2026-101918
PyPI	pyjwt	2.15.0	PYSEC-2026-4141
PyPI	pyjwt	2.15.0	GHSA-42vr-xj54-vc7v
Ubuntu:22.04:LTS	pyjwt	2.3.0-1ubuntu0.6	USN-8934-1
Ubuntu:22.04:LTS	pyjwt	2.3.0-1ubuntu0.6	UBUNTU-CVE-2026-101918
Ubuntu:24.04:LTS	pyjwt	2.7.0-1ubuntu0.4	USN-8934-1
Ubuntu:24.04:LTS	pyjwt	2.7.0-1ubuntu0.4	UBUNTU-CVE-2026-101918
Ubuntu:26.04:LTS	pyjwt	2.10.1-4ubuntu1.3	UBUNTU-CVE-2026-101918
Ubuntu:26.04:LTS	pyjwt	2.10.1-4ubuntu1.3	USN-8934-1
Ubuntu:26.10	pyjwt	2.13.0-1ubuntu1.1	USN-8934-1
Ubuntu:26.10	pyjwt	2.13.0-1ubuntu1.1	UBUNTU-CVE-2026-101918

Affected products (as reported)

Vendor	Product	Versions
jpadilla	pyjwt	>= 2.0.0a1, < 2.15.0

Weakness: CWE-248 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

https://github.com/jpadilla/pyjwt/security/advisories/GHSA-42vr-xj54-vc7v x_refsource_CONFIRM
https://github.com/jpadilla/pyjwt/commit/5fde08a6cf906aa7698de2d6391d88b73006b17b x_refsource_MISC
https://github.com/jpadilla/pyjwt/releases/tag/2.15.0 x_refsource_MISC