h3 before 2.0.1-rc.18 Open Redirect via redirectBack() (CVE-2026-86205) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-86205

h3 before 2.0.1-rc.18 Open Redirect via redirectBack()

Answer in brief

CVE-2026-86205 records a Unknown severity vulnerability in h3 before 2.0.1-rc.18 Open Redirect via redirectBack(). The current sources do not mark it as known exploited. The current feed maps h3js/h3 (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 6, 2026Updated Sep 6, 2026Source checked Sep 6, 2026First seen by HOL Sep 6, 2026Material review Sep 6, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps h3js/h3 (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
h3js/h3generic	>=2.0.1-rc.17 <2.0.1-rc.18	2.0.1-rc.18

Recommended response

Check inventory. Check lockfiles and deployed manifests for h3js/h3.
Review the reported fix. Update h3js/h3 to 2.0.1-rc.18 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 6, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 6, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 6, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.