CVE-2026-102265 PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header
An attacker can cause a denial of service by sending a deeply nested JWT token that triggers an unhandled RecursionError in PyJWT.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-102265?
CVE-2026-102265 is a medium-severity denial of service vulnerability in jpadilla pyjwt, published on 28 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWS._load in jwt/api_jws.py is affected because parser catches ValueError but not RecursionError. This occurs when a deeply nested token header reaches json.loads. As a result, RecursionError escapes the documented PyJWT error hierarchy. Consequently, an unauthenticated malformed token can cause a request-level failure and HTTP 500. This issue is fixed in version 2.14.0.
Weakness: CWE-674
Which versions are affected by CVE-2026-102265?
3 open source packages ship an affected version, including pyjwt and pyJWT. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pyjwt PyPI | From 2.13.0 | 2.14.0 |
pyjwt PyPI | From 2.13.0 | 2.14.0 |
pyJWT PyPI | From 2.13.0 | 2.14.0 |
Products include Pyjwt Project Pyjwt.
How do I fix CVE-2026-102265?
Upgrade pyjwt to 2.14.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-102265 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-102265 exists.
Other vulnerabilities in jpadilla pyjwt
- CVE-2026-102268 PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion guard
- CVE-2026-32597 PyJWT accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)
- CVE-2026-102266 PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation
- CVE-2026-102267 PyJWT: PyJWKClient follows redirects when fetching JWKS
- CVE-2026-102271 PyJWT: Public keys in DER form are accepted as HMAC secrets, bypassing the CVE-2022-29217 guard
Sources
Also known as AZL-105230, CLEANSTART-2026-GA98365, CLEANSTART-2026-PF22063, DEBIAN-CVE-2026-102265, ECHO-7f74-1f00-2375, GHSA-8wjv-2p76-3863 and 16 more.