CVE-2026-16117
Proxy rewrite bypass in @fastify/http-proxy allows encoded-prefixs to reach hidden upstream paths.
Is CVE-2026-16117 being exploited?
Not confirmed. CVE-2026-16117 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 0.44% probability of exploitation in the next 30 days.
How severe is CVE-2026-16117?
CVE-2026-16117 is rated Critical with a CVSS score of 10.0. 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-2026-16117?
Yes. A fix has been recorded for CVE-2026-16117. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16117 affect?
CVE-2026-16117 affects @fastify/http-proxy <= 11.5.0, Fastify-based reverse proxies, Node.js apps using rewritePrefix. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16117?
Upgrade @fastify/http-proxy to 11.6.0 immediately; audit proxies and block encoded-prefix requests.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attackers can bypass configured prefix rewrites by URL-encoding path segments to access upstream internal/admin endpoints, exposing hidden resources.
Immediate action required
- affected< 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.