@fastify/http-proxy vulnerable to prefix escape via backslash dot-segments (CVE-2026-85124) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-85124

@fastify/http-proxy vulnerable to prefix escape via backslash dot-segments

Answer in brief

CVE-2026-85124 records a Unknown severity vulnerability in @fastify/http-proxy vulnerable to prefix escape via backslash dot-segments. The current sources do not mark it as known exploited. The current feed maps @fastify/http-proxy/@fastify/http-proxy (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 3, 2026Updated Sep 3, 2026Source checked Sep 3, 2026First seen by HOL Sep 3, 2026Material review Sep 3, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps @fastify/http-proxy/@fastify/http-proxy (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
@fastify/http-proxy/@fastify/http-proxygeneric	>=0 <11.6.2	11.6.2

Recommended response

Check inventory. Check lockfiles and deployed manifests for @fastify/http-proxy/@fastify/http-proxy.
Review the reported fix. Update @fastify/http-proxy/@fastify/http-proxy to 11.6.2 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 3, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 3, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 3, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.