CVE-2026-33204: SimpleJWT has an Unauthenticated Denial of Service via JWE header tampering

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-20 · updated 2026-06-17
Weakness: CWE-400

Description

SimpleJWT is a simple JSON web token library written in PHP. Prior to version 1.1.1, an unauthenticated attacker can perform a Denial of Service via JWE header tampering when PBES2 algorithms are used. Applications that call JWE::decrypt() on attacker-controlled JWEs using PBES2 algorithms are affected. This issue has been patched in version 1.1.1.

Affected products

kelvinmo simplejwt: before 1.1.1 — fixed in 1.1.1

How to fix

Upgrade to a fixed version: kelvinmo simplejwt 1.1.1. Check the vendor advisory for mitigations.

References

https://github.com/kelvinmo/simplejwt/releases/tag/v1.1.1
https://github.com/kelvinmo/simplejwt/security/advisories/GHSA-xw36-67f8-339x

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