# CVE-2026-102270: PyJWT denial of service in PEM format validation

Source: https://junglewise.ai/threats/cve-2026-102270-pyjwt-is-a-python-implementation-of-json-web-token-standards  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-28. Updated: 2026-09-28  
License: CC BY 4.0 with a link back

CVE-2026-102270 · Severity: medium · CVSS 4.4 · Published 2026-09-28

PyJWT is a Python library for creating and validating JSON Web Tokens (JWTs), a standard security mechanism used in APIs and web applications. A flaw in the library's PEM format validation logic allows an attacker to craft a malicious certificate-like input that triggers excessive CPU consumption, potentially causing a denial of service. An affected application could become unresponsive or crash when processing a malicious JWT token.

Technologies: [Jpadilla PyJWT](https://junglewise.ai/threats/technologies/pyjwt), [pyjwt (PyPI)](https://junglewise.ai/threats/technologies/pypi-pyjwt). Vendors: [Jpadilla](https://junglewise.ai/threats/vendors/jpadilla), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-102270 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-102270 being exploited in the wild.

**How severe is CVE-2026-102270?** Medium severity, with a CVSS score of 4.4, published 28 September 2026.

**Which products and versions are affected?** Jpadilla PyJWT before 2.14.0; pyjwt (PyPI) <= 2.13.0, ECOSYSTEM:introduced=0,fixed=2.14.0.

**Is there a fix for CVE-2026-102270?** Yes. pyjwt (PyPI): upgrade to 2.14.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-102270 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-102270?** Check whether you run Jpadilla PyJWT or pyjwt (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- pyjwt (PyPI): upgrade to 2.14.0 or later

  ```sh
  pip install "pyjwt>=2.14.0"
  ```


## Technical details

The is_pem_format function in PyJWT uses a regular expression with lazy quantifiers that exhibits catastrophic backtracking when processing input containing repeated BEGIN markers without a matching END marker. An attacker can provide a certificate-like string that causes the regex engine to perform unbounded backtracking, resulting in CPU-intensive processing. The vulnerability is fixed by rejecting loader-accepted PEM variants and is resolved in version 2.14.0.

## Affected products

- jpadilla PyJWT before 2.14.0

## Identifiers

- CVE-2026-102270
- GHSA-jwrc-g2q2-pq5p
- PYSEC-2026-4148

## Timeline

- 2026-09-28: disclosed
- 2026-09-11: patched: Fix released in version 2.14.0

## References

- [https://github.com/jpadilla/pyjwt/commit/8b4e233a22206b34ec1186e912e75c0b2396ac07](https://github.com/jpadilla/pyjwt/commit/8b4e233a22206b34ec1186e912e75c0b2396ac07)
- [https://github.com/jpadilla/pyjwt/releases/tag/2.14.0](https://github.com/jpadilla/pyjwt/releases/tag/2.14.0)

## Related threats

- [PyJWT HS256/384/512 token forgery via empty HMAC key in oct JWK](https://junglewise.ai/threats/pyjwt-hs256-384-512-verify-accepts-empty-hmac-key-via-oct-jwk-pyjwk-a3ba63d2)
- [PyJWT decode() options-dict mutation enabling claim-verification bypass](https://junglewise.ai/threats/cve-2026-103001-pyjwt-decode-reintroduces-options-dict-mutation-enabling-silent)
- [PyJWT OKP algorithm key validation bypass](https://junglewise.ai/threats/cve-2026-102275-pyjwt-is-a-python-implementation-of-json-web-token-standards)
- [PyJWT unhandled ValueError in JWK Set parsing](https://junglewise.ai/threats/cve-2026-102274-pyjwt-is-a-python-implementation-of-json-web-token-standards)
- [PyJWT HMAC key validation bypass in HMACAlgorithm.prepare_key](https://junglewise.ai/threats/cve-2026-102273-pyjwt-is-a-python-implementation-of-json-web-token-standards)