Apply ReadHeaderTimeout when doing unencrypted HTTP/2 check in net/http (CVE-2026-56853) | HOL Guard CVE

High · CVSS 7.5CVE-2026-56853

Apply ReadHeaderTimeout when doing unencrypted HTTP/2 check in net/http

Answer in brief

CVE-2026-56853 records a High severity (CVSS 7.5) vulnerability in Apply ReadHeaderTimeout when doing unencrypted HTTP/2 check in net/http. The current sources do not mark it as known exploited. The current feed maps Go standard library/net/http (generic), stdlib (go). 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 13, 2026Updated Sep 24, 2026Source checked Sep 28, 2026First seen by HOL Aug 13, 2026Material review Sep 24, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.5
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.5. 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 Go standard library/net/http (generic), stdlib (go). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Go standard library/net/httpgeneric	>=0 <1.25.13 \|\| >=1.26.0-0 <1.26.6 \|\| >=1.27.0-0 <1.27.0-rc.3	1.25.13, 1.26.6, 1.27.0-rc.3
stdlibgo	>=0 <1.25.13 >=1.26.0-0 <1.26.6 >=1.27.0-0 <1.27.0-rc.3	1.25.13, 1.26.6, 1.27.0-rc.3

Recommended response

Check inventory. Check lockfiles and deployed manifests for Go standard library/net/http, stdlib.
Review the reported fix. Update Go standard library/net/http to 1.25.13; stdlib to 1.25.13 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 13, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 24, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 13, 2026

Sources and claim methodology

Upstream source description

When a server is configured to support unencrypted HTTP/2, it reads a few bytes from each new connection to see if they contain the HTTP/2 client preface. ReadHeaderTimeout is unexpectedly not being applied when doing this.

Quoted source text, attributed separately from HOL analysis.