CVE Catalog

CVE-2026-92395

CriticalCVSS 9.1
Published: Translated: NVD NIST

Summary

@fastify/proxy-addr versions 3.0.0 through 5.1.0 accept without error a trust subnet written in IPv4-mapped IPv6 notation with an IPv4-sized prefix (e.g. ::ffff:10.0.0.0/8 instead of ::ffff:10.0.0.0/104), causing every IPv4 address on the internet to be trusted. As a result, an unauthenticated client can supply an arbitrary X-Forwarded-For header and control the address the application reads. The issue is fixed in version 5.1.1.

Risk Assessment

It allows bypassing IP-based access control, rate limiting, geolocation, and audit logging. Any unauthenticated client can spoof any IP address, undermining trust in the application's security mechanisms.

Recommendation

Upgrade @fastify/proxy-addr to version 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.

Related vulnerabilities

Original NVD description (English source)

@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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS