Description

Shopware: Timing-attack on admin panel allowing enumeration of administrator usernames

Summary

There is a Proof of Concept which is able to enumerate the usernames of administrator users. This was possible by performing a timing attack.

Details

The faulty code exists in src/Core/Framework/Api/OAuth/UserRepository.php:

public function getUserEntityByUserCredentials(
        string $username,
        #[\SensitiveParameter]
        string $password,
        string $grantType,
        ClientEntityInterface $clientEntity
    ): ?UserEntityInterface {
        if ($this->loginConfigService->getConfig()?->useDefault === false) {...
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Subroutine getUserEntityByUserCredentials() is called when an auth request is send to api/oauth/token. If the given username is not found an early return is done (PATH 1). Only if the user is found we verify the password using password_verify.

PHP method password_verify by default uses hashing algorithm Argon2id which by design is intentionally 'slow' by introducing a timing cost to an attempt to bruteforce hashes more costly.

Since password_verify has a notable executable time, PATH 2 where an user is found and verified will be slower on average then PATH 1 where we do an early return for non-existing users.

Proposed fix

Before doing the early return, password_verify a dummy hash.

Impact

More targeted dictionary/bruteforce attacks.

Spear phishing / eases social engineering.

Credential stuffing from other data leaks.

Authors

Niel Duysters (@NielDuysters) and Thomas Brankaer (@tbrankaer)

Mitigation

Aliases

References