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CVE-2026-75975— fast-uri vulnerable to server-side request forgery via malformed IPv6 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.

Fastify fast-uri是Fastify团队的一个URI解析工具。 Fastify fast-uri 2.3.1至2.4.5之前版本、3.0.0至3.1.6之前版本和4.0.0至4.1.3之前版本存在安全漏洞，该漏洞源于对带括号的IPv6字面量的自定义解析器未验证完整IPv6语法，导致无效尾随文本被静默丢弃，攻击者控制的畸形主机被转换为不同的有效IPv6目标，可能导致服务端请求伪造和地址策略绕过。

CVSS 7.5 · High EPSS 0.22% · P12

Affected Version Matrix 6

VendorProduct Version RangeStatus
fast-uri fast-uri 2.3.1< 2.4.5 affected
2.4.5 unaffected
3.0.0< 3.1.6 affected
3.1.6 unaffected
4.0.0< 4.1.3 affected
4.1.3 unaffected
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I. Basic Information for CVE-2026-75975

Vulnerability Information
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Vulnerability Title
fast-uri vulnerable to server-side request forgery via malformed IPv6 normalization
Source: CVE Program / CVE List V5
Vulnerability Description
fast-uri is a URI parser for Node.js. Its custom parser for bracketed IPv6 literals does not validate the complete IPv6 grammar, so invalid trailing text in an authority can be silently discarded and a malformed attacker-controlled host is turned into a different valid IPv6 destination. For example, a bracketed literal with invalid trailing characters is normalized to the unspecified address, which a Node HTTP client then connects to a local service over loopback, and other malformed literals collapse to private-range addresses. No error is set on the parsed result, so an application checking the error field cannot detect the rewrite. An application that normalizes untrusted URLs before outbound requests, redirects, proxy routing, or address-policy enforcement can be redirected to a local or private IPv6 target, giving a server-side request forgery and address-policy bypass primitive. 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 validate bracketed IP literals against the full grammar and mark malformed literals as authority errors. 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
输入验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Fastify fast-uri 输入验证错误漏洞
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 2.3.1至2.4.5之前版本、3.0.0至3.1.6之前版本和4.0.0至4.1.3之前版本存在安全漏洞，该漏洞源于对带括号的IPv6字面量的自定义解析器未验证完整IPv6语法，导致无效尾随文本被静默丢弃，攻击者控制的畸形主机被转换为不同的有效IPv6目标，可能导致服务端请求伪造和地址策略绕过。
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 2.3.1 ~ 2.4.5 -

II. Public POCs for CVE-2026-75975

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8695 chars
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III. Intelligence Information for CVE-2026-75975

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Vendor Advisories for CVE-2026-75975 (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-2026-76172 7.5 HIGH fast-uri vulnerable to host confusion via percent-encoded scheme normalization

IV. Related Vulnerabilities

Same product: fast-uri
Same vendor: fast-uri
Same weakness: CWE-20

V. Comments for CVE-2026-75975

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