High, CVSS 7.5PackagistPublished
SimpleJWT has an Unauthenticated Denial of Service via JWE header tampering
CVE-2026-33204 · GHSA-xw36-67f8-339x
- Affected
- Packagist kelvinmo/simplejwt <= 1.1.0
- Fixed in
- 1.1.1· Vendor fix available
- Issue
- 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. Details PHP version: PHP 8.4.11 SimpleJWT version: v1.1.0 The relevant portion of the vulnerable implementation is shown below (PBES2.php): The security flaw lies in the lack of input validation when handling JWEs that uses PBES2. A "sanity ceiling" is not set on the iteration count, which is the parameter known in the JWE specification as p2c (RFC7518). The library calls decryptKey() with the untrusted input $headers which then use the PHP function hashpbkdf2() with the user-supplied value $headers['p2c']. This results in an algorithmic complexity denial-of-service (CPU exhaustion) because the PBKDF2 iteration count is fully attacker-controlled. Because the header is processed before successful decryption and authentication, the attack can be triggered using…
Recommended action: Upgrade to 1.1.1 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.