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[Security] Randomize CSRF token to harden BREACH attacks #39919

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Merged
merged 1 commit into from
Jan 23, 2021
Merged

[Security] Randomize CSRF token to harden BREACH attacks #39919

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1 change: 0 additions & 1 deletion src/Symfony/Bundle/SecurityBundle/Tests/Functional/CsrfFormLoginTest.php
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,6 @@ public function testFormLoginAndLogoutWithCsrfTokens($options)
$logoutLinks = $crawler->selectLink('Log out')->links();
$this->assertCount(2, $logoutLinks);
$this->assertStringContainsString('_csrf_token=', $logoutLinks[0]->getUri());
$this->assertSame($logoutLinks[0]->getUri(), $logoutLinks[1]->getUri());

$client->click($logoutLinks[0]);

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1 change: 1 addition & 0 deletions src/Symfony/Component/Security/CHANGELOG.md
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Expand Up @@ -4,6 +4,7 @@ CHANGELOG
5.3
---

* Randomize CSRF tokens to harden BREACH attacks
* Deprecated voters that do not return a valid decision when calling the `vote` method.

5.2.0
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35 changes: 32 additions & 3 deletions src/Symfony/Component/Security/Csrf/CsrfTokenManager.php
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Expand Up @@ -77,7 +77,7 @@ public function getToken(string $tokenId)
$this->storage->setToken($namespacedId, $value);
}

return new CsrfToken($tokenId, $value);
return new CsrfToken($tokenId, $this->randomize($value));
}

/**
Expand All @@ -90,7 +90,7 @@ public function refreshToken(string $tokenId)

$this->storage->setToken($namespacedId, $value);

return new CsrfToken($tokenId, $value);
return new CsrfToken($tokenId, $this->randomize($value));
}

/**
Expand All @@ -111,11 +111,40 @@ public function isTokenValid(CsrfToken $token)
return false;
}

return hash_equals($this->storage->getToken($namespacedId), $token->getValue());
return hash_equals($this->storage->getToken($namespacedId), $this->derandomize($token->getValue()));
}

private function getNamespace(): string
{
return \is_callable($ns = $this->namespace) ? $ns() : $ns;
}

private function randomize(string $value): string
{
$key = random_bytes(32);
$value = $this->xor($value, $key);

return sprintf('%s.%s.%s', substr(md5($key), 0, 1 + (\ord($key[0]) % 32)), rtrim(strtr(base64_encode($key), '+/', '-_'), '='), rtrim(strtr(base64_encode($value), '+/', '-_'), '='));
}

private function derandomize(string $value): string
{
$parts = explode('.', $value);
if (3 !== \count($parts)) {
return $value;
}
$key = base64_decode(strtr($parts[1], '-_', '+/'));
$value = base64_decode(strtr($parts[2], '-_', '+/'));

return $this->xor($value, $key);
}

private function xor(string $value, string $key): string
{
if (\strlen($value) > \strlen($key)) {
$key = str_repeat($key, ceil(\strlen($value) / \strlen($key)));
}

return $value ^ $key;
}
}
54 changes: 50 additions & 4 deletions src/Symfony/Component/Security/Csrf/Tests/CsrfTokenManagerTest.php
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Expand Up @@ -44,7 +44,7 @@ public function testGetNonExistingToken($namespace, $manager, $storage, $generat

$this->assertInstanceOf(CsrfToken::class, $token);
$this->assertSame('token_id', $token->getId());
$this->assertSame('TOKEN', $token->getValue());
$this->assertNotSame('TOKEN', $token->getValue());
}

/**
Expand All @@ -66,7 +66,34 @@ public function testUseExistingTokenIfAvailable($namespace, $manager, $storage)

$this->assertInstanceOf(CsrfToken::class, $token);
$this->assertSame('token_id', $token->getId());
$this->assertSame('TOKEN', $token->getValue());
$this->assertNotSame('TOKEN', $token->getValue());
}

/**
* @dataProvider getManagerGeneratorAndStorage
*/
public function testRandomizeTheToken($namespace, $manager, $storage)
{
$storage->expects($this->any())
->method('hasToken')
->with($namespace.'token_id')
->willReturn(true);

$storage->expects($this->any())
->method('getToken')
->with($namespace.'token_id')
->willReturn('TOKEN');

$values = [];
$lengths = [];
for ($i = 0; $i < 10; ++$i) {
$token = $manager->getToken('token_id');
$values[] = $token->getValue();
$lengths[] = \strlen($token->getValue());
}

$this->assertCount(10, array_unique($values));
$this->assertGreaterThan(2, \count(array_unique($lengths)));
}

/**
Expand All @@ -89,13 +116,33 @@ public function testRefreshTokenAlwaysReturnsNewToken($namespace, $manager, $sto

$this->assertInstanceOf(CsrfToken::class, $token);
$this->assertSame('token_id', $token->getId());
$this->assertSame('TOKEN', $token->getValue());
$this->assertNotSame('TOKEN', $token->getValue());
}

/**
* @dataProvider getManagerGeneratorAndStorage
*/
public function testMatchingTokenIsValid($namespace, $manager, $storage)
{
$storage->expects($this->exactly(2))
->method('hasToken')
->with($namespace.'token_id')
->willReturn(true);

$storage->expects($this->exactly(2))
->method('getToken')
->with($namespace.'token_id')
->willReturn('TOKEN');

$token = $manager->getToken('token_id');
$this->assertNotSame('TOKEN', $token->getValue());
$this->assertTrue($manager->isTokenValid($token));
}

/**
* @dataProvider getManagerGeneratorAndStorage
*/
public function testMatchingTokenIsValidWithLegacyToken($namespace, $manager, $storage)
{
$storage->expects($this->once())
->method('hasToken')
Expand Down Expand Up @@ -170,7 +217,6 @@ public function testNamespaced()

$token = $manager->getToken('foo');
$this->assertSame('foo', $token->getId());
$this->assertSame('random', $token->getValue());
}

public function getManagerGeneratorAndStorage()
Expand Down