CVE-2026-92395
Critical CVSS 9.1Published 2026-09-16 ยท last changed 2026-09-17
The fix
We hold no Microsoft remediation data for CVE-2026-92395, which normally means it is not a Windows CVE. For non-Microsoft software the fix is the vendor's own updated release, and the affected versions are listed below.
What it is
@fastify/proxy-addr is a Fastify plugin that determines a request's client address behind trusted reverse proxies, and it backs Fastify request.ip and request.ips. In versions 3.0.0 through 5.1.0, a trust subnet written in IPv4-mapped IPv6 notation with an IPv4-sized prefix, such as ::ffff:10.0.0.0/8 instead of the correct ::ffff:10.0.0.0/104, is accepted without error but trusts every IPv4 address on the internet rather than the block it names. Because the socket peer then becomes trusted at hop 0, any unauthenticated client can supply an arbitrary X-Forwarded-For header and control the address the application reads, which defeats IP-based access control, rate limiting, geolocation, and audit logging. The plugin inherited this defect from the upstream proxy-addr module (CVE-2026-90711). The issue is fixed in @fastify/proxy-addr 5.1.1, and users should upgrade to 5.1.1 or later. As a workaround, ensure any IPv4-mapped IPv6 trust subnet uses a prefix length of at least 97, or express the range in plain IPv4 notation.
Sources
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N