CVE-2026-15631
WebSocket path-traversal in @fastify/http-proxy allows bypassing rewrite prefix to reach unintended upstreams.
Is CVE-2026-15631 being exploited?
Not confirmed. CVE-2026-15631 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.33% probability of exploitation in the next 30 days.
How severe is CVE-2026-15631?
CVE-2026-15631 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-15631?
Yes. A fix has been recorded for CVE-2026-15631. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-15631 affect?
CVE-2026-15631 affects @fastify/http-proxy 9.4.0 - 11.5.0, Node.js applications using fastify http-proxy, WebSocketProxy.findUpstream code path. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-15631?
Upgrade @fastify/http-proxy to >=11.6.0 immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Path-traversal on WebSocket upgrade bypasses proxy rewrite, allowing attackers to reach unintended upstream endpoints via crafted upgrade requests (needs non-normalizing clients/proxies).
Patch when possible
- affected>= 9.4.0 and < 11.6.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.