Path traversal in Fastify-http-proxy - CVE-2026-15631
Published: July 20, 2026
Vulnerability identifier: #VU138401
CSH Severity: High
CVSS v4 BT: 6.9 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber]
CVE-ID: CVE-2026-15631
CWE-ID: CWE-22
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass the intended access boundary and disclose sensitive information.
The vulnerability exists due to path traversal in the WebSocket upstream URL construction in @fastify/http-proxy when processing a crafted WebSocket path containing .. segments. A remote attacker can send a specially crafted WebSocket upgrade request to bypass the intended access boundary and disclose sensitive information.
Only WebSocket endpoints on the upstream are reachable through this issue; HTTP-only paths at the escaped location do not complete the handshake.
Affected software
Fastify-http-proxy
How to mitigate CVE-2026-15631
Install security update from vendor's website.
Fastify-http-proxy - update to 11.6.0