CVE-2026-78659

HTTP/2 server memory exhaustion due to Trailer headers in net/http

Published Oct 8, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

Sign in to view the affected projects.

Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8935-1 Go vulnerabilities
History
Type Values Removed Values Added
Weaknesses CWE-399
CWE-770
Type Values Removed Values Added
Weaknesses CWE-405
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Go Standard Library
Go Standard Library net/http
Go Standard Library net/http2
Vendors & Products Go Standard Library
Go Standard Library net/http
Go Standard Library net/http2
Type Values Removed Values Added
Weaknesses CWE-399
CWE-770
Type Values Removed Values Added
Description 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.
Title HTTP/2 server memory exhaustion due to Trailer headers in net/http
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Go
Published
Updated
Oct 9, 2026, 3:34 PM
Reserved
Aug 24, 2026, 11:36 PM
Status
Awaiting Analysis
Published
Oct 8, 2026, 11:17 PM
Modified
Oct 9, 2026, 4:35 PM