7.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-33204

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

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.

(GitHub Advisory)

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CVE-2026-33204

CVE-2026-33204:

7.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
kelvinmo/simplejwt	composer	<= 1.1.0	1.1.1

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in the simplejwt library's handling of the PBES2 key management algorithm for JWE decryption. An unauthenticated attacker can craft a JWE with a malicious header containing an extremely large value for the p2c (PBKDF2 iteration count) parameter. The core of the vulnerability is in the SimpleJWT\Crypt\KeyManagement\PBES2::decryptKey function. In vulnerable versions, this function directly uses the p2c value from the untrusted JWE header without any validation. This value is then passed to the SimpleJWT\Crypt\KeyManagement\PBES2::generateKeyFromPassword function, which in turn uses it in a call to PHP's hash_pbkdf2 function. The hash_pbkdf2 function's execution time is directly proportional to the iteration count. By providing a very large number, an attacker can force the server to perform a computationally expensive key derivation, consuming significant CPU resources and blocking the process. This leads to a denial of service, as the server becomes unresponsive and legitimate requests cannot be processed. The patch, identified in commit 70ca5b6f0163f9f5da8e8ae8dce7d9f33b75fb90, addresses this by introducing a checkIterations method that validates the p2c value against a safe minimum and maximum range. This validation is applied in decryptKey before the value is used, effectively neutralizing the DoS vector. The setIterations method was also hardened as a preventative measure.

Vulnerable functions

SimpleJWT\Crypt\KeyManagement\PBES2::decryptKey

src/SimpleJWT/Crypt/KeyManagement/PBES2.php

This function is vulnerable because it processes the JWE header, including the attacker-controlled 'p2c' (iteration count) parameter, without proper validation. An attacker can provide an extremely large value for 'p2c', which is then passed to the key generation function, causing excessive CPU usage and a denial of service. The patch mitigates this by adding bounds checking on the 'p2c' value.

SimpleJWT\Crypt\KeyManagement\PBES2::generateKeyFromPassword

src/SimpleJWT/Crypt/KeyManagement/PBES2.php

This private function is where the core of the denial of service occurs. It takes the password and headers (containing the malicious 'p2c' value) and calls `hash_pbkdf2` to derive a key. The high iteration count from 'p2c' causes this function to consume excessive CPU resources, leading to the denial of service. Although private, it would likely appear in a detailed stack trace during exploitation.

SimpleJWT\Crypt\KeyManagement\PBES2::setIterations

src/SimpleJWT/Crypt/KeyManagement/PBES2.php

This public function was modified as part of the security hardening. While the primary attack vector is through the JWE header in `decryptKey`, this function could also have been used to set an excessively high iteration count programmatically. The patch adds the same validation to prevent this, making the class more robust against misuse.

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WAF Protection Rules

WAF Rule

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Reasoning

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