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CVE-2026-13676— fast-uri vulnerable to host confusion via failed IDN canonicalization

Quick assessment

Affected
fast-uri fast-uri
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.

fast-uri fast-uri是fast-uri的Web中间件。 fast-uri 2.3.1版本至3.1.2版本和4.0.0版本存在处理逻辑错误漏洞，该漏洞源于未能规范化HTTP系列URL的Unicode (IDN) 主机名。IDN转换路径调用了一个全局URL构造函数中不存在的辅助程序，导致主机名保持原始Unicode形式，而normalize()和equal()返回的值与WHATWG兼容的URL解析器不同。当应用使用fast-uri实施基于主机的策略（如黑名单、回环过滤、重定向验证、出站代理路由）

CVSS 7.5 · High EPSS 0.69% · P53

Affected Version Matrix 4

VendorProduct Version RangeStatus
fast-uri fast-uri 4.0.0< 4.0.1 affected
4.0.1 unaffected
2.3.1< 3.1.3 affected
3.1.3 unaffected
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I. Basic Information for CVE-2026-13676

Vulnerability Information
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Vulnerability Title
fast-uri vulnerable to host confusion via failed IDN canonicalization
Source: CVE Program / CVE List V5
Vulnerability Description
fast-uri versions 2.3.1 through 3.1.2 and 4.0.0 fail to canonicalize Unicode (IDN) hostnames for HTTP-family URLs. The IDN conversion path calls a helper that does not exist on the global URL constructor, silently leaving the host in its original Unicode form while normalize() and equal() still return values that differ from a WHATWG-compatible URL parser. Applications that use fast-uri to enforce host-based policy (denylists, loopback filtering, redirect validation, outbound proxy routing) before passing the same URL to Node's URL or fetch can be bypassed when the two implementations resolve the same input to different hosts. Patches: upgrade to fast-uri 3.1.3 for the 3.x line or 4.0.1 for the 4.x line. Workarounds: enforce host policy using the same URL parser used for the actual request, or reject non-ASCII hosts before policy checks.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
解释冲突
Source: CVE Program / CVE List V5
Vulnerability Title
Fastify fast-uri 处理逻辑错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
fast-uri fast-uri是fast-uri的Web中间件。 fast-uri 2.3.1版本至3.1.2版本和4.0.0版本存在处理逻辑错误漏洞，该漏洞源于未能规范化HTTP系列URL的Unicode (IDN) 主机名。IDN转换路径调用了一个全局URL构造函数中不存在的辅助程序，导致主机名保持原始Unicode形式，而normalize()和equal()返回的值与WHATWG兼容的URL解析器不同。当应用使用fast-uri实施基于主机的策略（如黑名单、回环过滤、重定向验证、出站代理路由）
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
fast-uri fast-uri 4.0.0 ~ 4.0.1 -

II. Public POCs for CVE-2026-13676

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 9992 chars
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III. Intelligence Information for CVE-2026-13676

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Vendor Advisories for CVE-2026-13676 (1)

IV. Related Vulnerabilities

Same product: fast-uri
Same vendor: fast-uri
Same weakness: CWE-436