CVE-2026-85124 PUBLISHED

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

Assigner: openjs
Reserved: 03.09.2026 Published: 03.09.2026 Updated: 03.09.2026

@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.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS Score: 7.5

Product Status

Vendor @fastify/http-proxy
Product @fastify/http-proxy
Versions Default: unaffected
  • affected from 0 to 11.6.2 (excl.)
  • Version 11.6.2 is unaffected

Credits

  • EQSTLab reporter
  • mcollina remediation developer
  • UlisesGascon remediation developer

References

Problem Types

  • CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') CWE