h2 allows HTTP Request Smuggling due to illegal characters in headers (CVE-2025-57804) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2025-57804GHSA-847F-9342-265H

h2 allows HTTP Request Smuggling due to illegal characters in headers

Answer in brief

CVE-2025-57804 records a Unknown severity vulnerability in h2 allows HTTP Request Smuggling due to illegal characters in headers. The current sources do not mark it as known exploited. The current feed maps h2 (pypi). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

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

Published Aug 25, 2025Updated Sep 10, 2026Source checked Sep 10, 2026First seen by HOL Sep 10, 2026Material review Sep 10, 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 h2 (pypi). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
h2pypi	>=0 <4.3.0	4.3.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for h2.
Review the reported fix. Update h2 to 4.3.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 25, 2025
Evidence: source:osv:source_dates:source-dates:record
Source modified
Sep 10, 2026
Evidence: source:osv:source_dates:source-dates:record
First seen by HOL
Sep 10, 2026

Sources and claim methodology

Upstream source description

### Summary HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls.

Quoted source text, attributed separately from HOL analysis.