@fastify/static vulnerable to route guard bypass via encoded path separators

published 2026-04-16 6 mo ago modified 2026-07-08 4 mo ago also GHSA-x428-ghpx-8j92 , EUVD-2026-23227

cvss: 5.9; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.4%; EPSS 0.4% chance of exploitation in 30 days, percentile 36%
public exploits: 0; none known

@fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's router treats them as literal characters. This mismatch allows attackers to bypass route-based middleware or guards that protect files served by @fastify/static. For example, a route guard on a protected path can be circumvented by encoding the path separator in the URL. Upgrade to @fastify/static 9.1.1 to fix this issue. There are no workarounds.

Patch / fix

fixed in 2

npm @fastify/static 9.1.1
@fastify/static @fastify/static 9.1.1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-6414 updated 2026-06-28 cvss 5.9

@fastify/static: @fastify/static: Security bypass via percent-encoded path separators

Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-cuda-rhel9, rhelai3/bootc-rocm-rhel9, rhelai3/disk-image-cuda-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-dashboard-rhel8, rhoai/odh-dashboard-rhel9, rhoai/odh-mod-arch-maas-rhel9, rhoai/odh-mod-arch-gen-ai-rhel9, rhoai/odh-mod-arch-model-registry-rhel9 Red Hat OpenShift Dev Spaces devspaces/dashboard-rhel9
affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 6 mo ago (2026-04-16)

Exploit prediction

0.42% chance of exploitation in the next 30 days, higher than 36% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.9	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
GitHub	3.1	5.9	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem	package	affected	fixed in
npm	@fastify/static	>=8.0.0, <9.1.1	9.1.1

Affected products

@fastify/static @fastify/static

Classification

Weakness

CWE-177 Improper Handling of URL Encoding (Hex Encoding)

References

github.com /fastify/fastify-static/security/advisories/GHSA-x428-ghpx-8j92
web, vendor-advisory
github.com /fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69p
web, not-applicable
github.com /honojs/hono/security/advisories/GHSA-q5qw-h33p-qvwr
web, not-applicable
cna.openjsf.org /security-advisories.html
web, third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2026-6414
advisory
github.com /fastify/fastify-static
package

Sources

CVE List CVE-2026-6414
GitHub Advisory GHSA-x428-ghpx-8j92
NVD CVE-2026-6414

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary