CVE-2021-29624

Lack of protection against cookie tossing attacks in fastify-csrf

Workarounds

None available.

References

1. https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Cheat_Sheet.html
2. https://owasp.org/www-pdf-archive/David_Johansson-Double_Defeat_of_Double-Submit_Cookie.pdf

Credits

This vulnerability was found by Xhelal Likaj [email protected].

For more information

If you have any questions or comments about this advisory:

• Open an issue in fastify-csrf
• Email us at [email protected]

Users that used fastify-csrf with the "double submit" mechanism using cookies with an application deployed across multiple subdomains, e.g. "heroku"-style platform as a service.

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-2021-29624 has a CVSS score of 6.5 (Medium). 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 (3.1.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Version 3.1.0 of the fastify-csrf fixes it.
See https://github.com/fastify/fastify-csrf/pull/51 and https://github.com/fastify/csrf/pull/2.

The user of the module would need to supply a userInfo when generating the CSRF token to fully implement the protection on their end. This is needed only for applications hosted on different subdomains.

1. What is CVE-2021-29624? CVE-2021-29624 is a medium-severity cross-site request forgery (CSRF) vulnerability in fastify-csrf (npm), affecting versions < 3.1.0. It is fixed in 3.1.0. 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-2021-29624? CVE-2021-29624 has a CVSS score of 6.5 (Medium). 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-csrf are affected by CVE-2021-29624? fastify-csrf (npm) versions < 3.1.0 is affected.
4. Is there a fix for CVE-2021-29624? Yes. CVE-2021-29624 is fixed in 3.1.0. Upgrade to this version or later.
5. Is CVE-2021-29624 exploitable, and should I be worried? Whether CVE-2021-29624 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-2021-29624 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-2021-29624? Upgrade fastify-csrf to 3.1.0 or later.

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