---
id: CVE-2026-120213
title: '@fastify/http-proxy vulnerable to prefix escape via decoded route parameters'
summary: >-
  @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 …
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'
cvssSource: cna
cwe:
  - CWE-22
  - CWE-436
vendor: '@fastify/http-proxy'
product: '@fastify/http-proxy'
affected:
  - '@fastify/http-proxy >= 9.0.0 < 11.6.6'
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-11-02T17:04:58.190785Z'
published: '2026-11-02'
updated: '2026-11-02'
sourceUpdated: '2026-11-02T17:05:17.281Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-120213'
references:
  - url: >-
      https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-h3vp-4jfr-v364
  - url: 'https://cna.openjsf.org/security-advisories.html'
tags:
  - cve.org
epss: 0.0069
epssPercentile: 0.53047
ingestedAt: '2026-11-05T19:30:42.720Z'
---

## Overview

@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.

## Affected

- `@fastify/http-proxy >= 9.0.0 < 11.6.6`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.