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CVE-2026-84394— fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority

Quick assessment

Affected
fast-uri fast-uri
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.

fast-uri 在解析主机名时，对于包含不成对或位置错误的方括号的 host 不会报错。如果一个 host 以左方括号 开头，但没有以右方括号 结尾，它既不会被验证为 IP 字面量，也不会被规范化为域名。因此， 会将该 host 直接返回，且 字段为 。与此同时，Node.js 的 及基于其构建的 HTTP 客户端会将同一字符串解析为不同的 host。如果应用程序读取解析后的 host 来做主机决策（例如 SSRF 黑名单、重定向白名单或代理路由），然后将原始 URL 传递给 HTTP 客户端，那么其策略所评估的

CVSS 7.5 · High

Possible ATT&CK Techniques 1 AI

T1200 · Hardware Additions
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I. Basic Information for CVE-2026-84394

Vulnerability Information
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Vulnerability Title
fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority
Source: CVE Program / CVE List V5
Vulnerability Description
fast-uri accepts a host that contains an unbalanced or misplaced authority bracket without reporting an error. A host that starts with an opening bracket but does not end with a closing bracket is neither validated as an IP literal nor canonicalized as a domain name, so parse() returns it as the host with error undefined, while Node's URL and the HTTP clients built on it resolve the same string to a different host. An application that reads the parsed host to make a host decision, such as an SSRF denylist, a redirect allowlist, or proxy routing, and then passes the original URL to an HTTP client evaluates its policy against a string that is not the host the request reaches. The same host is carried through normalize, equal, and resolve. This affects fast-uri versions 2.4.5, 3.1.6, and 4.1.3, and is fixed in 2.4.6, 3.1.7, and 4.1.4, where parse() reports a malformed host for any host that contains a bracket but is not a valid IPv6 literal.
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

Affected Products

Vendor Product Affected Versions CPE Subscribe
fast-uri fast-uri 2.4.5 ~ 2.4.6 -

II. Public POCs for CVE-2026-84394

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III. Intelligence Information for CVE-2026-84394

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Vendor Advisories for CVE-2026-84394 (1)

IV. Related Vulnerabilities

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

V. Comments for CVE-2026-84394

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