CyberRota Analysis
AI-GeneratedThe @fastify/proxy-addr plugin is vulnerable in versions 3.0.0 through 5.1.0, allowing unauthenticated clients to manipulate the X-Forwarded-For header due to improper handling of IPv4-mapped IPv6 notation, which can compromise IP-based access controls and logging. This critical vulnerability poses a significant risk to applications relying on accurate client IP identification, making it essential for developers and system administrators using affected versions to upgrade to 5.1.1 or later immediately. As a temporary measure, users should ensure that any IPv4-mapped IPv6 trust subnet has a prefix length of at least 97 or use plain IPv4 notation.
Public Exploit Signal
A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.
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Original NVD Description
@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.