CVE-2026-90711

proxy-addr vulnerable to IP spoofing via IPv4-mapped IPv6 trust subnet

Workarounds

Write IPv4 trust subnets in plain IPv4 notation (for example 10.0.0.0/8). If IPv4-mapped IPv6 notation is required, use the full form so the prefix covers the mapped marker (for example ::ffff:10.0.0.0/104 for the 10.0.0.0/8 block).

proxy-addr determines which network hops are trusted proxies so that X-Forwarded-For can be believed. When an application configures a trust subnet as an IPv4-mapped IPv6 address with a short prefix, such as ::ffff:10.0.0.0/8 (the correct spelling is ::ffff:10.0.0.0/104), the subnet compiles with all-zero leading bits and matches every IPv4 address instead of the block it names. The same happens for any IPv6 trust subnet with zero leading bits, such as ::/1.

Every unauthenticated client is then trusted as a proxy at hop 0, so proxyaddr(req, trust), and therefore req.ip and req.ips in Express, returns whatever the client sends in X-Forwarded-For. This defeats IP-based access control, rate limiting, geolocation, and audit logging. The misconfiguration compiles without any error, and the same block written correctly behaves correctly, so the difference is not visible from the configuration.

CVE-2026-90711 has a CVSS score of 9.1 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.0.8); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Upgrade to proxy-addr 2.0.8. An IPv4 address now matches an IPv6 trust subnet only when that subnet is a genuine IPv4-mapped subnet whose prefix covers the mapped marker.

1. What is CVE-2026-90711? CVE-2026-90711 is a critical-severity security vulnerability in proxy-addr (npm), affecting versions >= 1.1.0, < 2.0.8. It is fixed in 2.0.8.
2. How severe is CVE-2026-90711? CVE-2026-90711 has a CVSS score of 9.1 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of proxy-addr are affected by CVE-2026-90711? proxy-addr (npm) versions >= 1.1.0, < 2.0.8 is affected.
4. Is there a fix for CVE-2026-90711? Yes. CVE-2026-90711 is fixed in 2.0.8. Upgrade to this version or later.
5. Is CVE-2026-90711 exploitable, and should I be worried? Whether CVE-2026-90711 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-90711 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-90711? Upgrade proxy-addr to 2.0.8 or later.