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Prevent PKCE Downgrade Attack #1326

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merged 4 commits into from
Feb 15, 2023
Merged

Prevent PKCE Downgrade Attack #1326

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2a8c22c
Move code challenge verification to private function
Sephster Feb 15, 2023
c9255bd
StyleCI fix
Sephster Feb 15, 2023
1480564
Update changelog
Sephster Feb 15, 2023
0d523dd
Move pkce check so it happens prior to validation of code challenge
Sephster Feb 15, 2023
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4 changes: 4 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
### Added
- You can now set a leeway for time drift between servers when validating a JWT (PR #1304)

### Security
- Access token requests that contain a code_verifier but are not bound to a code_challenge will be rejected to prevent
a PKCE downgrade attack (PR #1326)

### [8.3.6] - released 2022-11-14
### Fixed
- Use LooseValidAt instead of StrictValidAt so that users aren't forced to use claims such as NBF in their JWT tokens (PR #1312)
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74 changes: 43 additions & 31 deletions src/Grant/AuthCodeGrant.php
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Original file line number Diff line number Diff line change
Expand Up @@ -127,39 +127,18 @@ public function respondToAccessTokenRequest(
throw OAuthServerException::invalidRequest('code', 'Cannot decrypt the authorization code', $e);
}

// Validate code challenge
if (!empty($authCodePayload->code_challenge)) {
$codeVerifier = $this->getRequestParameter('code_verifier', $request, null);

if ($codeVerifier === null) {
throw OAuthServerException::invalidRequest('code_verifier');
}
$codeVerifier = $this->getRequestParameter('code_verifier', $request, null);

// Validate code_verifier according to RFC-7636
// @see: https://tools.ietf.org/html/rfc7636#section-4.1
if (\preg_match('/^[A-Za-z0-9-._~]{43,128}$/', $codeVerifier) !== 1) {
throw OAuthServerException::invalidRequest(
'code_verifier',
'Code Verifier must follow the specifications of RFC-7636.'
);
}
// If a code challenge isn't present but a code verifier is, reject the request to block PKCE downgrade attack
if (empty($authCodePayload->code_challenge) && $codeVerifier !== null) {
throw OAuthServerException::invalidRequest(
'code_challenge',
'code_verifier received when no code_challenge is present'
);
}

if (\property_exists($authCodePayload, 'code_challenge_method')) {
if (isset($this->codeChallengeVerifiers[$authCodePayload->code_challenge_method])) {
$codeChallengeVerifier = $this->codeChallengeVerifiers[$authCodePayload->code_challenge_method];

if ($codeChallengeVerifier->verifyCodeChallenge($codeVerifier, $authCodePayload->code_challenge) === false) {
throw OAuthServerException::invalidGrant('Failed to verify `code_verifier`.');
}
} else {
throw OAuthServerException::serverError(
\sprintf(
'Unsupported code challenge method `%s`',
$authCodePayload->code_challenge_method
)
);
}
}
if (!empty($authCodePayload->code_challenge)) {
$this->validateCodeChallenge($authCodePayload, $codeVerifier);
}

// Issue and persist new access token
Expand All @@ -181,6 +160,39 @@ public function respondToAccessTokenRequest(
return $responseType;
}

private function validateCodeChallenge($authCodePayload, $codeVerifier)
{
if ($codeVerifier === null) {
throw OAuthServerException::invalidRequest('code_verifier');
}

// Validate code_verifier according to RFC-7636
// @see: https://tools.ietf.org/html/rfc7636#section-4.1
if (\preg_match('/^[A-Za-z0-9-._~]{43,128}$/', $codeVerifier) !== 1) {
throw OAuthServerException::invalidRequest(
'code_verifier',
'Code Verifier must follow the specifications of RFC-7636.'
);
}

if (\property_exists($authCodePayload, 'code_challenge_method')) {
if (isset($this->codeChallengeVerifiers[$authCodePayload->code_challenge_method])) {
$codeChallengeVerifier = $this->codeChallengeVerifiers[$authCodePayload->code_challenge_method];

if ($codeChallengeVerifier->verifyCodeChallenge($codeVerifier, $authCodePayload->code_challenge) === false) {
throw OAuthServerException::invalidGrant('Failed to verify `code_verifier`.');
}
} else {
throw OAuthServerException::serverError(
\sprintf(
'Unsupported code challenge method `%s`',
$authCodePayload->code_challenge_method
)
);
}
}
}

/**
* Validate the authorization code.
*
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71 changes: 71 additions & 0 deletions tests/Grant/AuthCodeGrantTest.php
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Original file line number Diff line number Diff line change
Expand Up @@ -917,6 +917,77 @@ public function testRespondToAccessTokenRequestCodeChallengeS256()
$this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
}

public function testPKCEDowngradeBlocked()
{
$client = new ClientEntity();
$client->setIdentifier('foo');
$client->setRedirectUri('http://foo/bar');
$client->setConfidential();
$clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
$clientRepositoryMock->method('getClientEntity')->willReturn($client);

$scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
$scopeEntity = new ScopeEntity();
$scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
$scopeRepositoryMock->method('finalizeScopes')->willReturnArgument(0);

$accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
$accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
$accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();

$refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
$refreshTokenRepositoryMock->method('persistNewRefreshToken')->willReturnSelf();
$refreshTokenRepositoryMock->method('getNewRefreshToken')->willReturn(new RefreshTokenEntity());

$grant = new AuthCodeGrant(
$this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
$this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
new DateInterval('PT10M')
);

$grant->setClientRepository($clientRepositoryMock);
$grant->setScopeRepository($scopeRepositoryMock);
$grant->setAccessTokenRepository($accessTokenRepositoryMock);
$grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
$grant->setEncryptionKey($this->cryptStub->getKey());
$grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));

$request = new ServerRequest(
[],
[],
null,
'POST',
'php://input',
[],
[],
[],
[
'grant_type' => 'authorization_code',
'client_id' => 'foo',
'redirect_uri' => 'http://foo/bar',
'code_verifier' => self::CODE_VERIFIER,
'code' => $this->cryptStub->doEncrypt(
\json_encode(
[
'auth_code_id' => \uniqid(),
'expire_time' => \time() + 3600,
'client_id' => 'foo',
'user_id' => 123,
'scopes' => ['foo'],
'redirect_uri' => 'http://foo/bar',
]
)
),
]
);

$this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
$this->expectExceptionCode(3);

/* @var StubResponseType $response */
$grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
}

public function testRespondToAccessTokenRequestMissingRedirectUri()
{
$client = new ClientEntity();
Expand Down