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CVE-2026-33805— @fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers

Quick assessment

Affected
@fastify/reply-from @fastify/reply-from
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/reply-from和fastify/http-proxy都是Fastify开源的产品。fastify/reply-from是一个插件，用于将传入的 HTTP 请求转发到另一个服务器。fastify/http-proxy是一个全功能 HTTP 代理插件，支持代理 WebSocket 和各种路由重定向。 fastify/reply-from 12.6.1及之前版本和fastify/http-proxy 11.4.3及之前版本存在安全漏洞，该漏洞源于在代理通过rewriteRequestHea

AI Predicted 7.5 Difficulty: Easy EPSS 0.44% · P37

Possible ATT&CK Techniques 1 AI

T1557 · Adversary-in-the-Middle

Affected Version Matrix 4

VendorProduct Version RangeStatus
@fastify/reply-from @fastify/http-proxy < 11.4.4 affected
11.4.4 unaffected
@fastify/reply-from @fastify/reply-from < 12.6.2 affected
12.6.2 unaffected
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I. Basic Information for CVE-2026-33805

Vulnerability Information
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Vulnerability Title
@fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers
Source: CVE Program / CVE List V5
Vulnerability Description
@fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders. This allows attackers to retroactively strip proxy-added headers from upstream requests by listing them in the Connection header value. Any header added by the proxy for routing, access control, or security purposes can be selectively removed by a client. @fastify/http-proxy is also affected as it delegates to @fastify/reply-from. Upgrade to @fastify/reply-from v12.6.2 or @fastify/http-proxy v11.4.4 or later.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
对HTTP头部进行脚本语法转义处理不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
fastify/reply-from和fastify/http-proxy 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
fastify/reply-from和fastify/http-proxy都是Fastify开源的产品。fastify/reply-from是一个插件，用于将传入的 HTTP 请求转发到另一个服务器。fastify/http-proxy是一个全功能 HTTP 代理插件，支持代理 WebSocket 和各种路由重定向。 fastify/reply-from 12.6.1及之前版本和fastify/http-proxy 11.4.3及之前版本存在安全漏洞，该漏洞源于在代理通过rewriteRequestHea
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

Vendor Product Affected Versions CPE Subscribe
@fastify/reply-from @fastify/reply-from 0 ~ 12.6.2 -
@fastify/reply-from @fastify/http-proxy 0 ~ 11.4.4 -

II. Public POCs for CVE-2026-33805

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III. Intelligence Information for CVE-2026-33805

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Vendor Advisories for CVE-2026-33805 (1)

IV. Related Vulnerabilities

Same product: @fastify/reply-from
Same vendor: @fastify/reply-from
Same weakness: CWE-644

V. Comments for CVE-2026-33805

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