# CVE-2026-86205

## Summary

- **CVE ID:** CVE-2026-86205
- **Severity:** MEDIUM
- **CVSS Score:** 5.4 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-601
- **Published:** Sep 6, 2026
- **Last Modified:** Sep 8, 2026

## 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.

## Affected Products

- h3js — h3 (2.0.1-rc.17)
- h3js — h3 (2.0.1-rc.18)

## References

- [CNA](https://github.com/h3js/h3/security/advisories/GHSA-fp4x-ggrf-wmc6)
- [CNA](https://www.vulncheck.com/advisories/h3-before-2.0.1-rc.18-open-redirect-via-redirectback)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.20%
- **EPSS Percentile:** 9.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._