Vulnerability Report

CVE-2026-15631

Title: WebSocket path traversal in @fastify/http-proxy

Arbitrary File Access

Proof Of Concept

No public PoC currently indexed for CVE-2026-15631.

CWE Category CWE-22
Published Date Jul 18, 2026
Modified Date Jul 28, 2026
Exploit Status Not Found
Score 8.7 CVSS v3.1
Exploit Probability (EPSS)
0.30%

Vulnerability Summary

CVE-2026-15631: Impact: @fastify/http-proxy versions from 9.4.0 up to and including 11.5.0 fail to validate the resolved WebSocket destination path against the configured rewrite prefix. The WebSocket routing path in WebSocketProxy.findUpstream resolves the destination via the WHATWG URL constructor, which collapses dot segments, so a crafted upgrade request with path traversal sequences can escape the rewrite prefix and reach upstream endpoints that were not meant to be exposed by the proxy. This is a variant of CVE-2021-21322 in a code path that never went through the HTTP fix in fastify/reply-from. Exploitation requires a non-normalizing WebSocket client, since browsers and the ws package normalize the request path before sending, but raw HTTP clients or downstream proxies that forward the request target unchanged make the attack reachable in production topologies. Patches: upgrade to @fastify/http-proxy 11.6.0. Workarounds: none.

Impacted Vendors

F
fastify 1

Reference Links

https://cna.openjsf.org/security-advisories.html https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-7hrw-592w-9wh2
CVSS v3.1
Source Entity [email protected]
Severity CRITICAL
10.0
Attack Vector
NETWORK
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
CHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
CVSS v3.1
Source Entity ce714d77-add3-4f53-aff5-83d477b104bb
Severity HIGH
8.7
Attack Vector
NETWORK
Complexity
HIGH
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
CHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2026-15631 Exploits & PoCs (Proof Of Concept)

No public PoCs found in our database for this CVE.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

Attack Vector Matrix

Access Vector NETWORK
Complexity LOW
Privileges N/A
Interaction NONE
CVSS Vector String CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Affected Stack

No specific products linked.