Medium severity5.4NVD Advisory· Published Sep 6, 2026· Updated Sep 8, 2026

CVE-2026-86205

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.

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References

github.com/h3js/h3/security/advisories/GHSA-fp4x-ggrf-wmc6nvd
www.vulncheck.com/advisories/h3-before-2.0.1-rc.18-open-redirect-via-redirectbacknvd

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cvss	0.351
epss	0.000
exploit	0.000
kev	0.000
patch	-0.070
ransomware	0.000