Review reviewCritical

CVE-2026-15631

@fastify/http-proxy @fastify/http-proxy, fastify/http-proxy

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. Expl...

CVSS: 10
EPSS: 0.33%
CISA KEV: Not listed
Published: 2026.07.18

PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability0.33%

Technical severityCVSS 10

Vulnerability overview

Affected product and versions

Product: @fastify/http-proxy @fastify/http-proxy, fastify/http-proxy
Affected versions: >= 9.4.0 < 11.6.0
Fixed versions: 11.6.0

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

1
Identify
Confirm that @fastify/http-proxy @fastify/http-proxy, fastify/http-proxy and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
CWE: CWE-22