CVE-2026-18427
@fastify/static vulnerable to route guard bypass via non-canonical path segments
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.
INFO
Published Date :
Aug. 6, 2026, 4:16 p.m.
Last Modified :
Aug. 6, 2026, 4:16 p.m.
Remotely Exploit :
No
Source :
ce714d77-add3-4f53-aff5-83d477b104bb
Affected Products
The following products are affected by CVE-2026-18427
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | ce714d77-add3-4f53-aff5-83d477b104bb |
Solution
- Update @fastify/static to version 10.1.3 or later.
- Ensure route guards correctly handle path canonicalization.
- Review use of the allowedPath option for static file serving.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-18427.
| URL | Resource |
|---|---|
| https://cna.openjsf.org/security-advisories.html | |
| https://github.com/fastify/fastify-static/security/advisories/GHSA-423g-23ch-w7c6 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-18427 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-18427
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-18427 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-18427 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by ce714d77-add3-4f53-aff5-83d477b104bb
Aug. 06, 2026
Action Type Old Value New Value Added Affected [{'vendor': '@fastify/static', 'product': '@fastify/static', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '10.1.3', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '10.1.3', 'versionType': 'semver'}], 'packageURL': 'pkg:npm/@fastify/static', 'defaultStatus': 'unaffected'}] Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Added CWE CWE-22 Added CWE CWE-436 Added Reference https://cna.openjsf.org/security-advisories.html Added Reference https://github.com/fastify/fastify-static/security/advisories/GHSA-423g-23ch-w7c6