Add permitted algorithms to validation context

examples/jwe-consume.php

@@ -9,6 +9,7 @@
 declare(strict_types = 1);
 
 use Sop\CryptoEncoding\PEM;
+use Sop\JWX\JWA\JWA;
 use Sop\JWX\JWK\RSA\RSAPrivateKeyJWK;
 use Sop\JWX\JWT\JWT;
 use Sop\JWX\JWT\ValidationContext;
@@ -21,7 +22,10 @@
 $jwk = RSAPrivateKeyJWK::fromPEM(
     PEM::fromFile(dirname(__DIR__) . '/test/assets/rsa/private_key.pem'));
 // create validation context containing only key for decryption
-$ctx = ValidationContext::fromJWK($jwk);
+$ctx = ValidationContext::fromJWK($jwk)
+    // NOTE: asymmetric key derivation algorithms are not enabled by default
+    // due to sign/encrypt confusion vulnerability!
+    ->withPermittedAlgorithmsAdded(JWA::ALGO_RSA1_5);
 // decrypt claims from the encrypted JWT
 $claims = $jwt->claims($ctx);
 // print all claims

lib/JWX/JWT/JWT.php

@@ -16,6 +16,7 @@
 use Sop\JWX\JWT\Header\Header;
 use Sop\JWX\JWT\Header\JOSE;
 use Sop\JWX\JWT\Parameter\ContentTypeParameter;
+use Sop\JWX\Parameter\Parameter;
 use Sop\JWX\Util\Base64;
 
 /**
@@ -161,7 +162,9 @@ public static function encryptedFromClaims(Claims $claims,
      */
     public function claims(ValidationContext $ctx): Claims
     {
-        // check signature or decrypt depending on the JWT type.
+        // check that the token uses only permitted algorithms
+        $this->_validateAlgorithms($ctx);
+        // check signature or decrypt depending on the JWT type
         if ($this->isJWS()) {
             $payload = self::_validatedPayloadFromJWS($this->JWS(), $ctx);
         } else {
@@ -338,6 +341,43 @@ private function _claimsFromNestedPayload(string $payload,
         return $jwt->claims($ctx);
     }
 
+    /**
+     * Validate that the token uses only permitted algorithms.
+     *
+     * @param ValidationContext $ctx Validation context
+     */
+    private function _validateAlgorithms(ValidationContext $ctx): void
+    {
+        $headers = $this->header();
+        if ($headers->hasAlgorithm()) {
+            $this->_validateAlgorithmParameter($headers->algorithm(), $ctx);
+        }
+        if ($headers->hasEncryptionAlgorithm()) {
+            $this->_validateAlgorithmParameter($headers->encryptionAlgorithm(), $ctx);
+        }
+        if ($headers->hasCompressionAlgorithm()) {
+            $this->_validateAlgorithmParameter($headers->compressionAlgorithm(), $ctx);
+        }
+    }
+
+    /**
+     * Check that given algorithm parameter value is permitted.
+     *
+     * @param Parameter         $param Header parameter
+     * @param ValidationContext $ctx   Validation context
+     *
+     * @throws ValidationException If algorithm is prohibited
+     */
+    private function _validateAlgorithmParameter(Parameter $param,
+        ValidationContext $ctx): void
+    {
+        if (!$ctx->isPermittedAlgorithm($param->value())) {
+            throw new ValidationException(sprintf(
+                '%s algorithm %s is not permitted.',
+                $param->name(), $param->value()));
+        }
+    }
+
     /**
      * Get validated payload from JWS.
      *

lib/JWX/JWT/ValidationContext.php

@@ -4,6 +4,7 @@
 
 namespace Sop\JWX\JWT;
 
+use Sop\JWX\JWA\JWA;
 use Sop\JWX\JWK\JWK;
 use Sop\JWX\JWK\JWKSet;
 use Sop\JWX\JWT\Claim\RegisteredClaim;
@@ -72,6 +73,54 @@ class ValidationContext
      */
     protected $_allowUnsecured;
 
+    /**
+     * List of permitted algorithms.
+     *
+     * By default only asymmetric key derivation algorithms are prohibited.
+     *
+     * @var string[]
+     */
+    protected $_permittedAlgoritms = [
+        // all signature algorithms are safe to use
+        JWA::ALGO_HS256 => true,
+        JWA::ALGO_HS384 => true,
+        JWA::ALGO_HS512 => true,
+        JWA::ALGO_RS256 => true,
+        JWA::ALGO_RS384 => true,
+        JWA::ALGO_RS512 => true,
+        JWA::ALGO_ES256 => true,
+        JWA::ALGO_ES384 => true,
+        JWA::ALGO_ES512 => true,
+        // unsecured JWS may be used when explicitly allowed
+        JWA::ALGO_NONE => true,
+        // all symmetric key derivation algorithms are safe to use
+        JWA::ALGO_A128KW => true,
+        JWA::ALGO_A192KW => true,
+        JWA::ALGO_A256KW => true,
+        JWA::ALGO_A128GCMKW => true,
+        JWA::ALGO_A192GCMKW => true,
+        JWA::ALGO_A256GCMKW => true,
+        JWA::ALGO_PBES2_HS256_A128KW => true,
+        JWA::ALGO_PBES2_HS384_A192KW => true,
+        JWA::ALGO_PBES2_HS512_A256KW => true,
+        JWA::ALGO_DIR => true,
+        /* asymmetric key derivation algorithms are subject to
+           "sign/encrypt confusion" vulnerability, in which the JWT consumer
+           can be tricked to accept a JWE token instead of a JWS by using
+           the public key for encryption. */
+        JWA::ALGO_RSA1_5 => false,
+        JWA::ALGO_RSA_OAEP => false,
+        // all encryption algorithms are safe to use
+        JWA::ALGO_A128CBC_HS256 => true,
+        JWA::ALGO_A192CBC_HS384 => true,
+        JWA::ALGO_A256CBC_HS512 => true,
+        JWA::ALGO_A128GCM => true,
+        JWA::ALGO_A192GCM => true,
+        JWA::ALGO_A256GCM => true,
+        // all compression algorithms are safe to use
+        JWA::ALGO_DEFLATE => true,
+    ];
+
     /**
      * Constructor.
      *
@@ -296,6 +345,65 @@ public function isUnsecuredAllowed(): bool
         return $this->_allowUnsecured;
     }
 
+    /**
+     * Get self with only given permitted algorithms.
+     *
+     * @param string ...$names Algorithm name
+     *
+     * @see \Sop\JWX\JWA\JWA
+     */
+    public function withPermittedAlgorithms(string ...$names): self
+    {
+        $obj = clone $this;
+        $obj->_permittedAlgoritms = [];
+        return $obj->withPermittedAlgorithmsAdded(...$names);
+    }
+
+    /**
+     * Get self with given algorithms added to the permitted set.
+     *
+     * @param string ...$names Algorithm name
+     *
+     * @see \Sop\JWX\JWA\JWA
+     */
+    public function withPermittedAlgorithmsAdded(string ...$names): self
+    {
+        $obj = clone $this;
+        foreach ($names as $name) {
+            $obj->_permittedAlgoritms[$name] = true;
+        }
+        return $obj;
+    }
+
+    /**
+     * Get self with given algorithms removed from the permitted set.
+     *
+     * @param string ...$names Algorithm name
+     *
+     * @see \Sop\JWX\JWA\JWA
+     */
+    public function withProhibitedAlgorithms(string ...$names): self
+    {
+        $obj = clone $this;
+        foreach ($names as $name) {
+            $obj->_permittedAlgoritms[$name] = false;
+        }
+        return $obj;
+    }
+
+    /**
+     * Check whether given algorithm is permitted.
+     *
+     * @param string $name Algorithm name
+     *
+     * @see \Sop\JWX\JWA\JWA
+     */
+    public function isPermittedAlgorithm(string $name): bool
+    {
+        return isset($this->_permittedAlgoritms[$name])
+            && true === $this->_permittedAlgoritms[$name];
+    }
+
     /**
      * Validate claims.
      *

test/unit/jwt/JWTTest.php

@@ -293,6 +293,17 @@ public function testInvalidJWT()
         new JWT('');
     }
 
+    public function testProhibitedAlgorithm()
+    {
+        $jwt = JWT::unsecuredFromClaims(
+            self::$_claims,
+            new Header(new JWTParameter(JWTParameter::P_ZIP, 'dummy'))
+        );
+        $this->expectException(ValidationException::class);
+        $this->expectExceptionMessage('zip algorithm dummy is not permitted');
+        $jwt->claims(new ValidationContext());
+    }
+
     /**
      * @depends testCreateJWS
      */

test/unit/jwt/ValidationContextTest.php

@@ -3,6 +3,7 @@
 declare(strict_types = 1);
 
 use PHPUnit\Framework\TestCase;
+use Sop\JWX\JWA\JWA;
 use Sop\JWX\JWT\Claim\IssuerClaim;
 use Sop\JWX\JWT\Claim\RegisteredClaim;
 use Sop\JWX\JWT\Claims;
@@ -157,4 +158,37 @@ public function testValidateRequiredFail(ValidationContext $ctx)
         $this->expectExceptionMessage('failed');
         $ctx->validate($claims);
     }
+
+    /**
+     * @depends testCreate
+     */
+    public function testAddPermittedAlgorithm(ValidationContext $ctx)
+    {
+        $this->assertTrue($ctx->isPermittedAlgorithm(JWA::ALGO_RS256));
+        $this->assertFalse($ctx->isPermittedAlgorithm('test'));
+        $ctx = $ctx->withPermittedAlgorithmsAdded('test');
+        $this->assertTrue($ctx->isPermittedAlgorithm(JWA::ALGO_RS256));
+        $this->assertTrue($ctx->isPermittedAlgorithm('test'));
+    }
+
+    /**
+     * @depends testCreate
+     */
+    public function testNewPermittedAlgorithm(ValidationContext $ctx)
+    {
+        $this->assertTrue($ctx->isPermittedAlgorithm(JWA::ALGO_RS256));
+        $ctx = $ctx->withPermittedAlgorithms('test');
+        $this->assertFalse($ctx->isPermittedAlgorithm(JWA::ALGO_RS256));
+        $this->assertTrue($ctx->isPermittedAlgorithm('test'));
+    }
+
+    /**
+     * @depends testCreate
+     */
+    public function testProhibitedAlgorithm(ValidationContext $ctx)
+    {
+        $this->assertTrue($ctx->isPermittedAlgorithm(JWA::ALGO_RS256));
+        $ctx = $ctx->withProhibitedAlgorithms(JWA::ALGO_RS256);
+        $this->assertFalse($ctx->isPermittedAlgorithm(JWA::ALGO_RS256));
+    }
 }