Description
@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.
Published: 2026-09-03
Score: 7.5 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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Remediation

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History

Thu, 03 Sep 2026 11:00:00 +0000

Type Values Removed Values Added
Description @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.
Title @fastify/http-proxy vulnerable to prefix escape via backslash dot-segments
Weaknesses CWE-22
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-09-03T12:32:56.358Z

Reserved: 2026-09-03T08:15:18.564Z

Link: CVE-2026-85124

cve-icon Vulnrichment

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cve-icon NVD

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cve-icon Redhat

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cve-icon OpenCVE Enrichment

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Weaknesses