The ProfileBasedRequestOptionsBuilder method returns allowedCredentials without any credentials if no username was found.
When WebAuthn is used as the first or only authentication method, an attacker can enumerate usernames based on the absence of the allowedCredentials property in the assertion options response. This allows enumeration of valid or invalid usernames.
return $this->publicKeyCredentialRequestOptionsFactory->create(
$this->profile,
count($allowedCredentials) <= 0 ? self::getRandomCredentials(): $allowedCredentials,
$optionsRequest->userVerification,
$extensions
);
private static function getRandomCredentials(): array
{
$credentialSources = [];
for ($i = 0; $i <= rand(0,1); $i++) {
$credentialSources[] = new PublicKeyCredentialSource(
random_bytes(32),
"public-key",
[],
"basic",
new EmptyTrustPath(),
Uuid::v7(),
random_bytes(77),
Uuid::v7()->__toString(),
rand(0, 6000),
null
);
}
return array_map(
static fn (PublicKeyCredentialSource $credential): PublicKeyCredentialDescriptor => $credential->getPublicKeyCredentialDescriptor(),
$credentialSources
);
}
By knowing which usernames are valid, attackers can focus their efforts on a smaller set of potential targets, increasing the efficiency and likelihood of successful attacks.
marcriemer Reporter
Summary
The ProfileBasedRequestOptionsBuilder method returns allowedCredentials without any credentials if no username was found.
Details
When WebAuthn is used as the first or only authentication method, an attacker can enumerate usernames based on the absence of the
allowedCredentialsproperty in the assertion options response. This allows enumeration of valid or invalid usernames.Proposal how to resolve it:
PoC
curl https://example.com/assertion/options
-H 'content-type: application/json'
--data-raw '{"username":"NotMeRandomUsername123"}'
Impact
By knowing which usernames are valid, attackers can focus their efforts on a smaller set of potential targets, increasing the efficiency and likelihood of successful attacks.