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CVE-2026-18446— fast-uri vulnerable to host confusion via backslash authority introducer

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。 Fastify fast-uri 4.1.2之前版本、3.1.5之前版本和2.4.4之前版本存在处理逻辑错误漏洞，该漏洞源于fast-uri与Node的URL解析器对反斜杠处理不一致，导致主机解析差异，可能被利用绕过基于主机的安全策略（如允许列表、SSRF过滤、重定向验证），将请求导向意外主机。

CVSS 7.5 · High EPSS 0.38% · P32

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 6

VendorProduct Version RangeStatus
fast-uri fast-uri 4.0.0< 4.1.2 affected
4.1.2 unaffected
3.0.0< 3.1.5 affected
3.1.5 unaffected
< 2.4.4 affected
2.4.4 unaffected
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I. Basic Information for CVE-2026-18446

Vulnerability Information
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Vulnerability Title
fast-uri vulnerable to host confusion via backslash authority introducer
Source: CVE Program / CVE List V5
Vulnerability Description
fast-uri before 4.1.2, 3.1.5, and 2.4.4 requires a literal double forward slash to recognize a URI authority, so a reference that uses a backslash based introducer in place of it (backslash backslash, forward slash backslash, or backslash forward slash) is parsed with no authority and folds into the path. Node's native WHATWG URL parser instead treats a backslash as interchangeable with a forward slash for special schemes, so the two parsers extract different hosts from the same input. Applications that use fast-uri to enforce host based policy such as allowlists, SSRF filtering, or redirect validation before passing the same URL into Node's URL or fetch consumers can be steered to an unintended host. Upgrade to fast-uri 4.1.2, 3.1.5, or 2.4.4.
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。 Fastify fast-uri 4.1.2之前版本、3.1.5之前版本和2.4.4之前版本存在处理逻辑错误漏洞，该漏洞源于fast-uri与Node的URL解析器对反斜杠处理不一致，导致主机解析差异，可能被利用绕过基于主机的安全策略（如允许列表、SSRF过滤、重定向验证），将请求导向意外主机。
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 ~ 4.1.2 -

II. Public POCs for CVE-2026-18446

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 6601 chars
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III. Intelligence Information for CVE-2026-18446

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Vendor Advisories for CVE-2026-18446 (1)

IV. Related Vulnerabilities

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