CVE-2026-15631: high-severity vulnerability in @fastify/http-proxy
@fastify/http-proxy vulnerable to prefix escape via WebSocket path traversal
Published · Updated
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 8.7epss 0.5%
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.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
Affected products
@fastify/http-proxy · @fastify/http-proxyRelated CVEs — @fastify/http-proxy
In the same product, most dangerous first.
CVE-2026-85124HIGH@fastify/http-proxy vulnerable to prefix escape via backslash dot-segmentsEPSS 0.7%CVE-2026-16117CRITICAL@fastify/http-proxy vulnerable to prefix escape via URL-encoded charactersEPSS 0.4%CVE-2026-120213CRITICAL@fastify/http-proxy vulnerable to prefix escape via decoded route parametersEPSS —CVE-2026-120214MEDIUM@fastify/http-proxy vulnerable to prefix escape via percent-encoded backslash dot-segmentsEPSS —