Bug 2529167 (CVE-2026-86205)

Summary: CVE-2026-86205 h3: h3: Open Redirect vulnerability via unsanitized Referer header
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in h3. This open redirect vulnerability exists in the `redirectBack()` utility, which fails to properly sanitize protocol-relative paths in the Referer header. A remote attacker can craft a specially designed URL that bypasses origin validation, leading to a redirect to an external, potentially malicious, domain. This could allow for phishing attacks or other malicious activities.
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Description OSIDB Bzimport 2026-09-06 12:12:06 UTC 
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.