Bug 2564951 (CVE-2026-120214)

Summary: CVE-2026-120214 @fastify/http-proxy: @fastify/http-proxy: Information disclosure via encoded backslash path traversal
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
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 vulnerability allows an unauthenticated remote attacker to cause information disclosure by bypassing intended proxy routing restrictions. Due to improper path validation that processes backslashes before decoding request paths, encoded backslashes and directory navigation sequences can pass uninspected. When requests are forwarded to an upstream server that treats backslashes as folder separators, attackers can retrieve sensitive resources outside the configured proxy directory.
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Description OSIDB Bzimport 2026-11-02 10:22:46 UTC 
@fastify/http-proxy is a Fastify plugin that proxies HTTP requests to an upstream server under a configured prefix. In versions 11.6.0 through 11.6.2, the destination validation normalizes literal backslashes before it percent-decodes the request path, so a path that encodes its backslashes and dot-segments survives the dot-segment check and is only turned into backslash and double-dot sequences after that check has passed. When the upstream resolves on a platform that treats a backslash as a path separator, the forwarded request walks out of the configured proxy prefix and reaches a sibling location on the upstream. An unauthenticated remote attacker can use this to retrieve upstream resources outside the intended prefix, so the impact is confidentiality only, and exploitation depends on the upstream's path handling. The issue is fixed in @fastify/http-proxy 11.6.3, and users should upgrade to 11.6.3 or later. This is a follow-up to the earlier prefix-escape fix, which did not account for the encoded-backslash form.