CVE-2026-18427
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk38th percentile - higher than 38% of all known CVEs
Summary
@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.
Risk Assessment
The risk is the disclosure of protected file contents, which could lead to leakage of sensitive data. The attack requires no authentication, so it can be carried out by anyone with access to the server.
Recommendation
It is recommended to update @fastify/static to version 10.1.3 or later. Also, review route guard configurations to ensure no other vulnerabilities exist.
Other vulnerabilities in @fastify/static
See all- CVE-2026-7120Medium
In @fastify/static before version 10.1.2, the allowedPath callback is evaluated before normalizing dot segments and duplicate path separators. An unauthenticated attacker can bypass allowedPath restrictions by requesting non-canonical paths, allowing files intended to be denied to be served.
- CVE-2026-15074High
The @fastify/static library up to version 10.1.0 fails to reject '..' path segments before file resolution. This allows bypassing path traversal protections and reading files inside the static root that are under a guarded URL prefix. The issue is patched in version 10.1.1.
Original NVD description (English source)
@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.