GHSA-875x-g8p7-5w27 The FIDO2/Webauthn Support for PHP library allows enumeration of valid usernames

• Packagist web-auth/webauthn-lib: >= 4.5.0, < 4.9.0 → fixed in 4.9.0 • Packagist web-auth/webauthn-framework: >= 4.5.0, < 4.9.0 → fixed in 4.9.0

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 `allowedCredentials` property in the assertion options response. This allows enumeration of valid or invalid usernames. Proposal how to resolve it: ``` return $this->publicKeyCredentialRequestOptionsFactory->create( $this->profile, count($allowedCredentials) userVerification, $extensions ); private static function getRandomCredentials(): array { $credentialSources = []; for ($i = 0; $i __toString(), rand(0, 6000), null ); } return array_map( static fn (PublicKeyCredentialSource $credential): PublicKeyCredentialDescriptor => $credential->getPublicKeyCredentialDescriptor(), $credentialSources ); } ``` 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.