CVE-2023-31999

@fastify/oauth2 vulnerable to Cross Site Request Forgery due to reused Oauth2 state

Workarounds

There are no known workarounds.

References

• Prevent Attacks and Redirect Users with OAuth 2.0 State Parameters

All versions of @fastify/oauth2 used a statically generated state parameter at startup time and were used across all requests for all users.
The purpose of the Oauth2 state parameter is to prevent Cross-Site-Request-Forgery attacks. As such, it should be unique per user and should be connected to the user's session in some way that will allow the server to validate it.

A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones. Typical impact: state-changing actions performed as the victim without their consent.

CVE-2023-31999 has a CVSS score of 7.4 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (7.2.0); upgrading removes the vulnerable code path.

Kodem intelligence

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v7.2.0 changes the default behavior to store the state in a cookie with the http-only and same-site=lax attributes set. The state is now by default generated for every user.

Note that this contains a breaking change in the checkStateFunction function, which now accepts the full Request object.

1. What is CVE-2023-31999? CVE-2023-31999 is a high-severity cross-site request forgery (CSRF) vulnerability in @fastify/oauth2 (npm), affecting versions < 7.2.0. It is fixed in 7.2.0. A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones.
2. How severe is CVE-2023-31999? CVE-2023-31999 has a CVSS score of 7.4 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of @fastify/oauth2 are affected by CVE-2023-31999? @fastify/oauth2 (npm) versions < 7.2.0 is affected.
4. Is there a fix for CVE-2023-31999? Yes. CVE-2023-31999 is fixed in 7.2.0. Upgrade to this version or later.
5. Is CVE-2023-31999 exploitable, and should I be worried? Whether CVE-2023-31999 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-31999 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-31999? Upgrade @fastify/oauth2 to 7.2.0 or later.