h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked Cookie (CVE-2026-86250) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-86250

h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked Cookie

Answer in brief

CVE-2026-86250 records a Unknown severity vulnerability in h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked Cookie. 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	>=2.0.0-beta.4 <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 fail to validate the chunk count parsed from user-controlled cookie values in setChunkedCookie() and deleteChunkedCookie() functions. Attackers can send a crafted cookie header with an extremely large chunk count to trigger an O(n²) cleanup loop that hangs the server process.

Quoted source text, attributed separately from HOL analysis.