CVE-2024-31999

@fastify/secure-session: Reuse of destroyed secure session cookie

Workarounds

Include a "last update" field in the session, and treat "old sessions" as expired.
Make sure to configure your cookie as "http only".

References

• https://hackerone.com/reports/2374253

At the end of the request handling, it will encrypt all data in the session with a secret key and attach the ciphertext as a cookie value with the defined cookie name. After that, the session on the server side is destroyed. When an encrypted cookie with matching session name is provided with subsequent requests, it will decrypt the ciphertext to get the data. The plugin then creates a new session with the data in the ciphertext. Thus theoretically the web instance is still accessing the data from a server-side session, but technically that session is generated solely from a user provided cookie (which is assumed to be non-craftable because it is encrypted with a secret key not known to the user).

The issue exists in the session removal process. In the delete function of the code, when the session is deleted, it is marked for deletion. However, if an attacker could gain access to the cookie, they could keep using it forever.

CVE-2024-31999 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 (7.3.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Fixed in 56d66642ecc633cff0606927601e81cdac361370.
Update to v7.3.0.

1. What is CVE-2024-31999? CVE-2024-31999 is a high-severity security vulnerability in @fastify/secure-session (npm), affecting versions < 7.3.0. It is fixed in 7.3.0.
2. How severe is CVE-2024-31999? CVE-2024-31999 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/secure-session are affected by CVE-2024-31999? @fastify/secure-session (npm) versions < 7.3.0 is affected.
4. Is there a fix for CVE-2024-31999? Yes. CVE-2024-31999 is fixed in 7.3.0. Upgrade to this version or later.
5. Is CVE-2024-31999 exploitable, and should I be worried? Whether CVE-2024-31999 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-2024-31999 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-2024-31999? Upgrade @fastify/secure-session to 7.3.0 or later.