@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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||
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| @fastify/http-proxy | @fastify/http-proxy | unaffected |
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Mon, 02 Nov 2026 10:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | @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. | |
| Title | @fastify/http-proxy vulnerable to prefix escape via decoded route parameters | |
| Weaknesses | CWE-22 CWE-436 |
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cvssV3_1
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MITRE
Status: PUBLISHED
Assigner: openjs
Published:
Updated: 2026-11-02T10:15:08.777Z
Reserved: 2026-10-31T13:33:29.612Z
Link: CVE-2026-120213
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