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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 在 2.0.1-rc.18 之前的版本中，其 工具函数存在一个开放重定向漏洞。该漏洞的原因是未能对 Referer 头中的协议相对路径（protocol-relative paths）进行过滤处理。攻击者可以构造一个同源 URL，其中包含双斜杠路径段（如 ）。这个路径段能够通过与原始 Referer 相同的协议和域名而通过源校验，但生成的 头会被浏览器解析为指向外部域名的协议相对重定向。

CVSS 5.4 · Medium

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

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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