Vulnerability · Published Sep 3, 2026 · Assigned by openjs
CVE-2026-85124@fastify/http-proxy vulnerable to prefix escape via backslash dot-segments
High 7.5
In plain English
A high-severity path traversal in @fastify/http-proxy from @fastify/http-proxy. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 55% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| @fastify/http-proxy | @fastify/http-proxy | 0 – before 11.6.2 |
Weakness: CWE-22 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N