fastify http-proxy up to 11.5.0 Prefix Rewrite request.url replace prefix input validation

Summaryinfo

A vulnerability was found in fastify http-proxy up to 11.5.0. It has been declared as critical. The affected element is the function replace of the file request.url of the component Prefix Rewrite. Such manipulation of the argument prefix leads to input validation. This vulnerability is listed as CVE-2026-16117. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability was found in fastify http-proxy up to 11.5.0. It has been rated as critical. Affected by this issue is the function replace of the file request.url of the component Prefix Rewrite. The manipulation of the argument prefix with an unknown input leads to a input validation vulnerability. Using CWE to declare the problem leads to CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-16117 since 07/17/2026. The exploitation is known to be easy. The attack may be launched remotely. Technical details are known, but there is no available exploit.

Upgrading to version 11.6.0 eliminates this vulnerability.

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Productinfo

Type

• Firewall Software

Vendor

• fastify

Name

• http-proxy

Version

• 11.0
• 11.1
• 11.2
• 11.3
• 11.4
• 11.5.0

CPE 2.3info

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CPE 2.2info

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