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CVE-2026-120213: Fastify HTTP-Proxy can let attackers bypass path restrictions

CVE-2026-120213 · published 7 days ago

Summary

The Fastify HTTP-Proxy plugin versions 9.0.0 through 11.6.5 let a remote user change the destination path by using specially crafted URL parts. This could allow access to parts of the upstream server that should be blocked, possibly leading to unauthorized actions. Upgrade the plugin to version 11.6.6 or newer to stop this behavior.

What to do

Update @fastify/http-proxy @fastify/http-proxy to version 11.6.6 or later.

Affected software

Vendor	Product	Affected versions
@fastify/http-proxy	@fastify/http-proxy	< 11.6.6

Original advisory text

@fastify/http-proxy vulnerable to prefix escape via decoded route parameters

@fastify/http-proxy is a Fastify plugin that proxies HTTP requests to an upstream server under a configured prefix. In versions 9.0.0 through 11.6.5, when an application uses parameterized prefix and rewritePrefix options to pin clients to a fixed upstream path, the plugin substitutes URL-decoded route parameters into rewritePrefix without re-encoding them. A parameter value that encodes a path separator together with a fragment or query delimiter therefore decodes into real separators and delimiters that inject extra upstream path segments and strip the mandatory suffix the rewritePrefix was meant to enforce, without using any dot-dot traversal. An unauthenticated remote attacker can use this to reach upstream locations outside the intended prefix, leading to path-restriction bypass and, depending on the upstream, server-side request forgery or authorization bypass in the proxied service. The issue is fixed in @fastify/http-proxy 11.6.6, and users should upgrade to 11.6.6 or later. There is no workaround other than upgrading.

References

https://cna.openjsf.org/security-advisories.html Vendor Advisory
https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/120xxx/CVE-2026-1202... Vendor Advisory
https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-h3vp-4jfr... Vendor Advisory
https://nvd.nist.gov/vuln/detail/CVE-2026-120213 Vendor Advisory

Fix within

Internet-facing 3 days

Internal 60 days

Not known to be exploited
Can be exploited automatically
Gives an attacker full control

Severity

9.1 Critical

Exploitation

<1% chance of attack within 30 days

Type

CWE-22Path Traversal

CWE-436Interpretation Conflict

Timeline

Published2 Nov 2026

Updated9 Nov 2026

First seen2 Nov 2026

Sources

CVE-2026-120213 · NVD

CVE-2026-120213 · MITRE

CVE-2026-120213 · OSV

GHSA-h3vp-4jfr-v364 · GHSA

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