Bug 2527955 (CVE-2026-85124)

Summary: CVE-2026-85124 @fastify/http-proxy: @fastify/http-proxy: Information disclosure via path traversal with backslash dot-segments
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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. This component, designed to proxy HTTP requests, does not correctly validate incoming request paths, specifically failing to account for backslash-based dot-segments. An unauthenticated network attacker can exploit this vulnerability to bypass the proxy's path restrictions. This allows them to access internal network endpoints that should be protected, leading to the disclosure of sensitive information.
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Description OSIDB Bzimport 2026-09-03 11:04:22 UTC 
@fastify/http-proxy versions before 11.6.2 do not validate proxied HTTP request paths for backslash based dot-segments before forwarding them to the configured upstream. The plain HTTP request handler skips the destination validation that the WebSocket path performs, and the underlying reply-from library only rejects forward-slash traversal, so a request containing backslash dot-segments can escape the boundary set by the prefix and rewritePrefix options. An unauthenticated network attacker can use this to reach upstream paths that were meant to stay hidden behind the proxy, resulting in disclosure of internal endpoints. This is a path traversal issue (CWE-22). Users should upgrade to @fastify/http-proxy 11.6.2 or later.