Go net/http Unencrypted HTTP/2 Preface Read Skips ReadHeaderTimeout (<1.25.13, 1.26.0<1.26.6, 1.27.0
CVE-2026-56853 Published on August 13, 2026
Apply ReadHeaderTimeout when doing unencrypted HTTP/2 check in net/http
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.
Products Associated with CVE-2026-56853
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Affected Versions
Go standard library net/http:- Before 1.25.13 is affected.
- Version 1.26.0-0 and below 1.26.6 is affected.
- Version 1.27.0-0 and below 1.27.0-rc.3 is affected.