Bug 2564955 (CVE-2026-120213)

Summary: CVE-2026-120213 @fastify/http-proxy: @fastify/http-proxy vulnerable to prefix escape via decoded route parameters
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedCC: sdawley
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in @fastify/http-proxy. When applications configure path rewriting using route parameters, the plugin fails to re-encode decoded URL parameters before constructing upstream request paths. An unauthenticated remote attacker can exploit this flaw by sending requests containing encoded path separators or query delimiters to bypass intended path restrictions. This allows the attacker to reach arbitrary endpoints on upstream servers, potentially leading to Server-Side Request Forgery (SSRF) or unauthorized access to internal services.
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Description OSIDB Bzimport 2026-11-02 10:23:56 UTC 
@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.