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CVE-2026-92395— @fastify/proxy-addr vulnerable to IP spoofing via IPv4-mapped IPv6 trust subnet

Quick assessment

Affected
@fastify/proxy-addr @fastify/proxy-addr
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

@fastify/proxy-addr 是一个 Fastify 插件，用于确定经过受信任的反向代理后的请求客户端地址，它支撑着 Fastify 的 和 。在 3.0.0 到 5.1.0 版本中，以 IPv4 映射的 IPv6 记法编写的信任子网，若使用了 IPv4 大小的前缀（例如使用 而非正确的 ），会被无误地接受，但它信任的是互联网上所有的 IPv4 地址，而非其所命名的地址块。由于套接字对端（socket peer）在跳转 0 时被判定为受信任，任何未经身份验证的客户端都可以通过提供一个任意的 头来控制应用程

CVSS 9.1 · Critical

Possible ATT&CK Techniques 1 AI

T1557 · Adversary-in-the-Middle
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I. Basic Information for CVE-2026-92395

Vulnerability Information
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Vulnerability Title
@fastify/proxy-addr vulnerable to IP spoofing via IPv4-mapped IPv6 trust subnet
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用欺骗进行的认证绕过
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
@fastify/proxy-addr @fastify/proxy-addr 3.0.0 ~ 5.1.1 -

II. Public POCs for CVE-2026-92395

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III. Intelligence Information for CVE-2026-92395

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Vendor Advisories for CVE-2026-92395 (1)

IV. Related Vulnerabilities

Same weakness: CWE-290

V. Comments for CVE-2026-92395

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