CVE-2026-16732— fastify vulnerable to X-Forwarded-* spoofing under trustProxy hop-count
Quick assessment
Affected
fastify fastify
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是Fastify团队开源的一个高性能的Node.js Web框架。 Fastify 5.8.3至5.12.1之前版本存在信任管理问题漏洞，该漏洞源于对转发请求头的信任管理不当，可能导致攻击者绕过前端代理直接访问Fastify并伪造转发请求字段，造成主机注入、HTTPS强制绕过、安全Cookie和CSRF来源绕过、基于主机的路由和缓存中毒。
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I. Basic Information for CVE-2026-16732
Vulnerability Information
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Vulnerability Title
fastify vulnerable to X-Forwarded-* spoofing under trustProxy hop-count
Source: CVE Program / CVE List V5
Vulnerability Description
fastify is a fast and low overhead web framework for Node.js. Impact: the fix for CVE-2026-3635 added a guard on the forwarded-header reads used to derive the request host, protocol, hostname, ip, and ips values, checking the connecting address. That guard closes the IP, CIDR, and custom-function forms of trustProxy correctly, because those forms compile to predicates that inspect the connecting address. The hop-count form, where trustProxy is set to a number, compiles to a predicate that structurally ignores the address, so the guard is always satisfied for any hop count of one or more. Applications configured with a numeric trustProxy value, such as trustProxy set to 1 for a single reverse proxy, remain vulnerable: an attacker who can reach the Fastify origin directly, bypassing the front-facing proxy, can spoof the forwarded request fields exactly as in the unpatched version. The impact class matches the parent CVE-2026-3635, including host injection in generated URLs, HTTPS-enforcement bypass, secure-cookie and CSRF-origin bypass, and host-based routing and cache poisoning. Affected versions are fastify from 5.8.3 up to but not including 5.12.1. Patches: patched in fastify 5.12.1, where the numeric form of trustProxy is disabled at runtime and removed from the TypeScript type union. Workarounds: migrate to an IP, CIDR, or custom-function trustProxy value that validates the connecting address, and ensure the Fastify origin is only reachable through the trusted proxy chain.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用不可信的源
Source: CVE Program / CVE List V5
Vulnerability Title
Fastify 信任管理问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Fastify是Fastify团队开源的一个高性能的Node.js Web框架。 Fastify 5.8.3至5.12.1之前版本存在信任管理问题漏洞，该漏洞源于对转发请求头的信任管理不当，可能导致攻击者绕过前端代理直接访问Fastify并伪造转发请求字段，造成主机注入、HTTPS强制绕过、安全Cookie和CSRF来源绕过、基于主机的路由和缓存中毒。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
II. Public POCs for CVE-2026-16732
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Vendor Advisories for CVE-2026-16732 (1)
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