Description
Impact: @fastify/http-proxy versions up to and including 11.5.0 fail to rewrite the request prefix when the prefix segment is URL-encoded. Fastify's router URL-decodes paths for route matching, but request.url retains the original encoded form, and the prefix-rewrite step uses a literal string replace against the decoded prefix. A request that encodes one or more characters of the configured prefix therefore matches the route but skips the rewrite, so the raw encoded path is forwarded to the upstream unchanged. The upstream then decodes the path and serves it, letting an attacker reach upstream paths that the proxy was configured to hide via rewritePrefix, including internal or administrative endpoints.

Patches: upgrade to @fastify/http-proxy 11.6.0.

Workarounds: none.
Published: 2026-07-18
Score: 10 Critical
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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History

Tue, 28 Jul 2026 21:00:00 +0000

Type Values Removed Values Added
First Time appeared Fastify
Fastify fastify-http-proxy
Vendors & Products Fastify
Fastify fastify-http-proxy

Mon, 20 Jul 2026 16:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Sat, 18 Jul 2026 13:45:00 +0000

Type Values Removed Values Added
Description Impact: @fastify/http-proxy versions up to and including 11.5.0 fail to rewrite the request prefix when the prefix segment is URL-encoded. Fastify's router URL-decodes paths for route matching, but request.url retains the original encoded form, and the prefix-rewrite step uses a literal string replace against the decoded prefix. A request that encodes one or more characters of the configured prefix therefore matches the route but skips the rewrite, so the raw encoded path is forwarded to the upstream unchanged. The upstream then decodes the path and serves it, letting an attacker reach upstream paths that the proxy was configured to hide via rewritePrefix, including internal or administrative endpoints. Patches: upgrade to @fastify/http-proxy 11.6.0. Workarounds: none.
Title @fastify/http-proxy vulnerable to prefix escape via URL-encoded characters
Weaknesses CWE-20
References
Metrics cvssV3_1

{'score': 10, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N'}


Subscriptions

Fastify Fastify-http-proxy
cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-07-20T15:14:49.004Z

Reserved: 2026-07-17T15:40:14.822Z

Link: CVE-2026-16117

cve-icon Vulnrichment

Updated: 2026-07-20T15:14:44.605Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-07-28T20:39:32Z

Weaknesses