Vulnerability Description
@fastify/static before version 10.1.3 contains an incomplete fix for a previous route guard bypass. The static file handler rejected only parent directory segments, but it did not canonicalize dot segments, duplicate slashes, encoded dots, or backslashes before route matching and before delegating to the send layer. As a result, an unauthenticated attacker could request a file protected by a route based guard using a non canonical path form that misses the guarded route yet resolves back onto the protected file, disclosing its contents. Applications that protect a subtree of the static root with a route based guard are affected, while applications relying on the allowedPath option are not. This is fixed in @fastify/static 10.1.3, which canonicalizes the pathname, including rejecting backslashes, on the path used for routing and serving.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://cna.openjsf.org/security-advisories.html
- https://github.com/fastify/fastify-static/security/advisories/GHSA-423g-23ch-w7c
FAQ
What is CVE-2026-18427?
CVE-2026-18427 is a vulnerability with a CVSS score of 7.5 (HIGH). @fastify/static before version 10.1.3 contains an incomplete fix for a previous route guard bypass. The static file handler rejected only parent directory segments, but it did not canonicalize dot seg...
How severe is CVE-2026-18427?
CVE-2026-18427 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-18427?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.