Go net/http HTTP/2 Trailer Header Memory Exhaustion
CVE-2026-78659 Published on October 8, 2026
HTTP/2 server memory exhaustion due to Trailer headers in net/http
When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead. For HTTP/2 servers, a malicious client can exploit this by sending a "Trailer" header that declares a large number of fields, causing the server to allocate a disproportionate amount of memory while bypassing Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits. This exploit is not applicable for HTTP/1 servers, which do not support multiplexing a large number of requests over one TCP connection, and whose Server.MaxHeaderBytes are calculated differently.
Vulnerability Analysis
CVE-2026-78659 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
What is an Amplification Vulnerability?
Software that does not appropriately monitor or control resource consumption can lead to adverse system performance. This situation is amplified if the software allows malicious users or attackers to consume more resources than their access level permits. Exploiting such a weakness can lead to asymmetric resource consumption, aiding in amplification attacks against the system or the network.
CVE-2026-78659 has been classified to as an Amplification vulnerability or weakness.
Products Associated with CVE-2026-78659
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Affected Versions
Go standard library net/http:- Before 1.26.9 is affected.
- Version 1.27.0-0 and below 1.27.2 is affected.
- Before 0.60.0 is affected.