CVE-2024-39912: Enumeration of valid usernames in web-auth/webauthn-lib

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-07-15 · updated 2026-06-17
Weakness: CWE-204

Description

web-auth/webauthn-lib is an open source set of PHP libraries and a Symfony bundle to allow developers to integrate that authentication mechanism into their web applications. 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. 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. This issue has been addressed in version 4.9.0 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

Affected products

Spomky-Labs Webauthn Framwork: from 4.5.0 before 4.9.0 — fixed in 4.9.0

How to fix

Upgrade to a fixed version: Spomky-Labs Webauthn Framwork 4.9.0. Check the vendor advisory for mitigations.

References

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