URL Redirection to Untrusted Site ('Open Redirect') in fastify-static

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2021-22963: 1.17% estimated exploitation activity in the next 30 days; percentile 67.44 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact 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//google.com/%2e%2e. The issue shows up on all the fastify-static applications that set redirect: true option. By default, it is false. Patches The issue has been patched in fastify-static@4.2.4 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

Published by the source

5 Oct 2021, 20:24 UTC

Last modified by the source

8 Nov 2023, 04:05 UTC

Source last checked

26 Oct 2026, 12:21 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-p6vg-p826-qp3v

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-p6vg-p826-qp3v

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# Patch Next advisory brief: CVE-2021-22963

Advisory: URL Redirection to Untrusted Site ('Open Redirect') in fastify-static
IDs: CVE-2021-22963, GHSA-p6vg-p826-qp3v
Record: https://patchnext.com/advisories/cve-2021-22963 (revision 2, source checked 26 Oct 2026, 12:21 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fastify-static 4.2.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm fastify-static: affected < 4.2.4; fixed in 4.2.4

## Suggested inspection (read-only)
- `npm ls fastify-static --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on fastify-static.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-p6vg-p826-qp3v (OSV record GHSA-p6vg-p826-qp3v lists affected ranges: npm fastify-static >=0 <4.2.4 (fixed))
- Verified: https://github.com/advisories/GHSA-p6vg-p826-qp3v (GitHub-reviewed advisory GHSA-p6vg-p826-qp3v lists affected ranges: npm fastify-static >=0 <4.2.4)

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