Description
@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.
Published: 2026-11-02
Score: 5.9 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

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History

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 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.
Title @fastify/http-proxy vulnerable to prefix escape via percent-encoded backslash dot-segments
Weaknesses CWE-22
References
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N'}


Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-11-02T10:07:08.695Z

Reserved: 2026-10-31T14:04:08.530Z

Link: CVE-2026-120214

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-11-02T11:17:31.277

Modified: 2026-11-02T16:18:52.027

Link: CVE-2026-120214

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-11-02T11:30:14Z

Weaknesses
  • CWE-22

    Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')