Vulnerability · Published Sep 28, 2026 · Assigned by GitHub_M

CVE-2026-102270PyJWT: ReDoS vulnerability when calling the `is_pem_format` function.

Medium 4.4

In plain English

A medium-severity regular-expression denial of service in pyjwt from jpadilla. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.4Medium

Exploit odds (30 days)0.2%top 84.1% 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. Prior to 2.14.0, PyJWT is_pem_format is affected because lazy PEM regular expression backtracks extensively. This occurs when a certificate-like input contains repeated BEGIN markers without a matching END marker. As a result, is_pem_format performs unbounded backtracking while searching for a PEM end marker. Consequently, an attacker can cause intensive CPU consumption. This issue is fixed in version 2.14.0.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	pyjwt	no fix listed	DEBIAN-CVE-2026-102270
Debian:13	pyjwt	no fix listed	DEBIAN-CVE-2026-102270
Debian:14	pyjwt	2.14.0-1	DEBIAN-CVE-2026-102270
PyPI	pyjwt	2.14.0	GHSA-jwrc-g2q2-pq5p
PyPI	pyjwt	2.14.0	PYSEC-2026-4148
Ubuntu:26.10	pyjwt	no fix listed	UBUNTU-CVE-2026-102270

Affected products (as reported)

Vendor	Product	Versions
jpadilla	pyjwt	< 2.14.0

Weakness: CWE-1333 · Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jwrc-g2q2-pq5p x_refsource_CONFIRM
https://github.com/jpadilla/pyjwt/commit/8b4e233a22206b34ec1186e912e75c0b2396ac07 x_refsource_MISC
https://github.com/jpadilla/pyjwt/releases/tag/2.14.0 x_refsource_MISC