CVE-2026-56853: Go Standard Library Net/http

High severity, CVSS 7.5. EPSS: 0.6% chance of exploitation in the next 30 days.

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.

Affected products

• Go Standard Library Net/http: before 1.25.13 (fixed in 1.25.13); from 1.26.0-0, before 1.26.6 (fixed in 1.26.6); from 1.27.0-0, before 1.27.0-rc.3 (fixed in 1.27.0-rc.3)

Published 2026-08-13. Last modified 2026-09-03.