CVE-2021-22964

DOS and Open Redirect with user input

Workarounds

If updating is not an option, you can sanitize the input URLs using the rewriteUrl server option.

References

• Bug founder: drstrnegth
• hackerone Report

For more information

If you have any questions or comments about this advisory:

• Open an issue in fastify-static
• Contact the security team

A redirect vulnerability in the fastify-static module allows remote attackers to redirect Mozilla Firefox users to arbitrary websites via a double slash // followed by a domain: http://localhost:3000//a//youtube.com/%2e%2e%2f%2e%2e.

A DOS vulnerability is possible if the URL contains invalid characters curl --path-as-is "http://localhost:3000//^/.."

The issue shows up on all the fastify-static applications that set redirect: true option. By default, it is false.

Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.

CVE-2021-22964 has a CVSS score of 8.8 (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 (4.4.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

The issue has been patched in [email protected]

1. What is CVE-2021-22964? CVE-2021-22964 is a high-severity open redirect vulnerability in fastify-static (npm), affecting versions >= 4.2.4, < 4.4.1. It is fixed in 4.4.1. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
2. How severe is CVE-2021-22964? CVE-2021-22964 has a CVSS score of 8.8 (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-static are affected by CVE-2021-22964? fastify-static (npm) versions >= 4.2.4, < 4.4.1 is affected.
4. Is there a fix for CVE-2021-22964? Yes. CVE-2021-22964 is fixed in 4.4.1. Upgrade to this version or later.
5. Is CVE-2021-22964 exploitable, and should I be worried? Whether CVE-2021-22964 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-2021-22964 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-2021-22964? Upgrade fastify-static to 4.4.1 or later.

Other vulnerabilities in fastify-static