CVE-2026-18427

@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 v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact NONE

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://cna.openjsf.org/security-advisories.html	Third Party Advisory
https://github.com/fastify/fastify-static/security/advisories/GHSA-423g-23ch-w7c6	Mitigation Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:fastify:fastify-static:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-08-06 16:16

Updated : 2026-09-04 18:16

NVD link : CVE-2026-18427

Mitre link : CVE-2026-18427

CVE.ORG link : CVE-2026-18427

JSON object : View

Products Affected

fastify

fastify-static

CWE

CWE-22

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

CWE-436

Interpretation Conflict

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