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CVE-2026-86205— h3 before 2.0.1-rc.18 Open Redirect via redirectBack()

Quick assessment

Affected
h3js h3
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.

H3是H3组织开源的一个HTTP框架。 H3 2.0.1-rc.18之前版本存在输入验证错误漏洞，该漏洞源于redirectBack()实用程序未能清理Referer标头中的协议相对路径，攻击者可利用双斜杠路径段绕过同源验证，导致浏览器将Location标头解释为指向外部域名的协议相对重定向。

CVSS 5.4 · Medium EPSS 0.27% · P18

Possible ATT&CK Techniques 1 AI

T1084

Affected Version Matrix 2

VendorProduct Version RangeStatus
h3js h3 2.0.1-rc.17< 2.0.1-rc.18 affected
2.0.1-rc.18 unaffected
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I. Basic Information for CVE-2026-86205

Vulnerability Information
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Vulnerability Title
h3 before 2.0.1-rc.18 Open Redirect via redirectBack()
Source: CVE Program / CVE List V5
Vulnerability Description
h3 versions before 2.0.1-rc.18 contain an open redirect vulnerability in the redirectBack() utility that fails to sanitize protocol-relative paths in the Referer header pathname. Attackers can craft a same-origin URL with a double-slash path segment that passes origin validation but produces a Location header interpreted by browsers as a protocol-relative redirect to an external domain.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
指向未可信站点的URL重定向(开放重定向)
Source: CVE Program / CVE List V5
Vulnerability Title
H3 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
H3是H3组织开源的一个HTTP框架。 H3 2.0.1-rc.18之前版本存在输入验证错误漏洞，该漏洞源于redirectBack()实用程序未能清理Referer标头中的协议相对路径，攻击者可利用双斜杠路径段绕过同源验证，导致浏览器将Location标头解释为指向外部域名的协议相对重定向。
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
h3js h3 2.0.1-rc.17 ~ 2.0.1-rc.18 -

II. Public POCs for CVE-2026-86205

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III. Intelligence Information for CVE-2026-86205

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Vendor Advisories for CVE-2026-86205 (2)

Same Patch Batch · h3js · 2026-09-06 · 5 CVEs total

CVE-2026-86250 7.5 HIGH h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked Cookie
CVE-2026-86251 5.9 MEDIUM h3 before 1.15.9 Path Traversal via Double Decoding
CVE-2026-86253 5.9 MEDIUM h3 before 1.15.6 Path Traversal via Percent-Encoded Dot Segments
CVE-2026-86252 5.3 MEDIUM h3 before 1.15.9 SSE Event Injection via Carriage Return

IV. Related Vulnerabilities

Same product: h3
Same vendor: h3js
Same weakness: CWE-601

V. Comments for CVE-2026-86205

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