---
id: CVE-2026-86205
title: >-
  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
summary: >-
  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 …
severity: medium
cvss: 5.4
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N'
cwe:
  - CWE-601
vendor: h3js
product: h3
affected:
  - h3 >= 2.0.1-rc.17 < 2.0.1-rc.18
published: '2026-09-06'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T20:00:18.870'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-86205'
references:
  - url: 'https://github.com/h3js/h3/security/advisories/GHSA-fp4x-ggrf-wmc6'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/h3-before-2.0.1-rc.18-open-redirect-via-redirectback
    label: disclosure@vulncheck.com
  - url: 'https://github.com/h3js/h3/security/advisories/GHSA-fp4x-ggrf-wmc6'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-86205.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-86205'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2529167'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-86205'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-86205'
tags:
  - nvd
  - cve.org
  - exploit-available
  - csaf
  - vex
  - red-hat
epss: 0.00197
epssPercentile: 0.09772
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-08T13:28:03.688110Z'
ingestedAt: '2026-09-07T03:04:07.439Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat OpenShift AI (RHOAI) · no fix planned: Red Hat OpenShift AI (RHOAI) · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-86205.json)