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CVE-2026-16158— @fastify/reply-from vulnerable to cross-upstream request routing via URL cache key collision

Quick assessment

Affected
@fastify/reply-from @fastify/reply-from
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Fastify @fastify/reply-from是Fastify团队的一款Web中间件服务器。 Fastify @fastify/reply-from 8.3.1至12.6.4之前版本存在服务端请求伪造漏洞，该漏洞源于在构建内部URL缓存键时未使用分隔符连接目标和源路径，可能导致跨上游数据访问和修改。

CVSS 8.7 · High EPSS 0.38% · P30

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 2

VendorProduct Version RangeStatus
@fastify/reply-from @fastify/reply-from 8.3.1< 12.6.4 affected
12.6.4 unaffected
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I. Basic Information for CVE-2026-16158

Vulnerability Information
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Vulnerability Title
@fastify/reply-from vulnerable to cross-upstream request routing via URL cache key collision
Source: CVE Program / CVE List V5
Vulnerability Description
Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4 build the internal URL cache key by concatenating the destination and source path without a delimiter. Different destination and source pairs can therefore produce the same key while resolving to different upstream URLs. When getUpstream selects an upstream from request data, a URL cached for one upstream can be reused for a request intended for another upstream, causing cross-upstream data access and modification. The default configuration is affected. Setting disableCache to true prevents the behavior. Patches: upgrade to @fastify/reply-from 12.6.4. Workarounds: pass disableCache: true when registering the plugin.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
未有动机的代理或中间人(混淆代理)
Source: CVE Program / CVE List V5
Vulnerability Title
Fastify @fastify/reply-from 服务端请求伪造漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Fastify @fastify/reply-from是Fastify团队的一款Web中间件服务器。 Fastify @fastify/reply-from 8.3.1至12.6.4之前版本存在服务端请求伪造漏洞，该漏洞源于在构建内部URL缓存键时未使用分隔符连接目标和源路径，可能导致跨上游数据访问和修改。
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 8.3.1 ~ 12.6.4 -

II. Public POCs for CVE-2026-16158

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Reproduced successfully in a real sandbox · Below is the actual recording of building the environment and exploiting the vulnerability.
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claude_code · 11922 chars
GitHub 复现环境（可 clone 直接跑）
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POC zip download
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III. Intelligence Information for CVE-2026-16158

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Vendor Advisories for CVE-2026-16158 (1)

IV. Related Vulnerabilities

Same product: @fastify/reply-from
Same vendor: @fastify/reply-from
Same weakness: CWE-441

V. Comments for CVE-2026-16158

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