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CVE-2026-76172— fast-uri vulnerable to host confusion via percent-encoded scheme normalization

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 是用于 Node.js 的 URI 解析器。在解析过程中，它会对 URI 的 scheme（协议）部分执行一次遗留的解码操作，且不再对解码结果进行重新转义；而序列化时，scheme 部分会原样输出，这与主机（host）组件的处理方式不同（主机组件会被重新转义）。因此，对于 scheme 中包含经过百分号编码的斜杠字符（ 或 ）的输入，解析后得到的 scheme 没有 Authority 部分，导致解析结果中的主机（host）和错误信息均为 undefined。然而，对该输入进行解析或标准化（nor

CVSS 7.5 · High

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-76172

Vulnerability Information
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Vulnerability Title
fast-uri vulnerable to host confusion via percent-encoded scheme normalization
Source: CVE Program / CVE List V5
Vulnerability Description
fast-uri is a URI parser for Node.js. During parsing it runs a legacy decoding pass over the scheme component and never re-escapes the result, and serialization writes the scheme back out verbatim, unlike the host component which is re-escaped. As a result an input whose scheme carries percent-encoded slashes parses as a scheme with no authority, so the parsed host and error are both undefined, yet resolving or normalizing that same input emits a network-path reference whose authority is attacker-chosen and re-parses to that host. An application that allowlists on the parsed host, or treats a reference with no authority as safe to resolve against its base, gets the opposite of what it checked, giving an off-site redirect, server-side request forgery, or address-policy bypass. The legacy decoder also expands non-standard escape forms, widening the issue past upstream filters, and control characters in the scheme can reach the output as raw carriage return and line feed. The affected versions are 2.3.1 up to but not including 2.4.5, 3.0.0 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which reject a scheme that is not valid after decoding. Users should upgrade to a patched version.
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
URL编码处理不恰当(Hex编码)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
fast-uri fast-uri 2.3.1 ~ 2.4.5 -

II. Public POCs for CVE-2026-76172

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 10407 chars
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III. Intelligence Information for CVE-2026-76172

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Vendor Advisories for CVE-2026-76172 (1)

Same Patch Batch · fast-uri · 2026-08-24 · 4 CVEs total

CVE-2026-75899 7.5 HIGH fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding
CVE-2026-75931 7.5 HIGH fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative
CVE-2026-75975 7.5 HIGH fast-uri vulnerable to server-side request forgery via malformed IPv6 normalization

IV. Related Vulnerabilities

Same product: fast-uri
Same vendor: fast-uri
Same weakness: CWE-177

V. Comments for CVE-2026-76172

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