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.
Vulnerability Analysis
CVE-2026-56853 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
Allocation of Resources Without Limits or Throttling
The software allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor.
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.