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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.

Fastify fast-uri是Fastify团队的一个URI解析工具。 Fastify fast-uri 2.4.5版本、3.1.6版本和4.1.3版本存在处理逻辑错误漏洞，该漏洞源于对含不平衡或错位方括号的主机验证不当，可能导致应用程序在安全决策（如SSRF黑名单、重定向白名单或代理路由）中评估错误主机，从而绕过安全策略。

CVSS 7.5 · High EPSS 0.38% · P32

Possible ATT&CK Techniques 1 AI

T1200 · Hardware Additions

Affected Version Matrix 6

VendorProduct Version RangeStatus
fast-uri fast-uri 2.4.5< 2.4.6 affected
2.4.6 unaffected
3.1.6< 3.1.7 affected
3.1.7 unaffected
4.1.3< 4.1.4 affected
4.1.4 unaffected
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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
Vulnerability Title
Fastify fast-uri 处理逻辑错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Fastify fast-uri是Fastify团队的一个URI解析工具。 Fastify fast-uri 2.4.5版本、3.1.6版本和4.1.3版本存在处理逻辑错误漏洞，该漏洞源于对含不平衡或错位方括号的主机验证不当，可能导致应用程序在安全决策（如SSRF黑名单、重定向白名单或代理路由）中评估错误主机，从而绕过安全策略。
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 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