CVE-2024-39912 is a medium-severity (CVSS 5.3) CWE-204 vulnerability in web-auth/webauthn-lib. A fix is available for web-auth/webauthn-lib — see the affected versions and patch details below.
Enumeration of valid usernames in web-auth/webauthn-lib
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2024-39912.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2024-39912 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
web-auth/webauthn-lib🐘web-auth/webauthn-frameworkReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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) <= 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
);
}
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | web-auth/webauthn-lib | ≥ 4.5.0&&< 4.9.0 | 4.9.0composer require web-auth/webauthn-lib:^4.9.0 |
| 🐘Packagist | web-auth/webauthn-framework | ≥ 4.5.0&&< 4.9.0 | 4.9.0composer require web-auth/webauthn-framework:^4.9.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for web-auth/webauthn-lib, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update web-auth/webauthn-lib to 4.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-39912 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2024-39912 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2024-39912. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2024-39912 in your dependencies?
O3 Security finds CVE-2024-39912 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.