CVE-2026-16117

@fastify/http-proxy vulnerable to prefix escape via URL-encoded characters

Published Jul 18, 2026 CVSS 3.1 · 10 Critical EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Fastify
Fastify fastify-http-proxy
Vendors & Products Fastify
Fastify fastify-http-proxy
Type Values Removed Values Added
Metrics ssvc

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

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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
openjs
Published
Updated
Jul 20, 2026, 3:14 PM
Reserved
Jul 17, 2026, 3:40 PM
Status
Analyzed
Published
Jul 18, 2026, 2:17 PM
Modified
Jul 28, 2026, 3:39 PM