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.
Metrics
Affected Vendors & Products
References
History
Fri, 09 Oct 2026 18:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-399 CWE-770 |
Fri, 09 Oct 2026 16:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-405 | |
| Metrics |
cvssV3_1
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Fri, 09 Oct 2026 09:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Go Standard Library
Go Standard Library net/http Go Standard Library net/http2 |
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| Vendors & Products |
Go Standard Library
Go Standard Library net/http Go Standard Library net/http2 |
Fri, 09 Oct 2026 01:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-399 CWE-770 |
Thu, 08 Oct 2026 23:00:00 +0000
| 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 |
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Status: PUBLISHED
Assigner: Go
Published: 2026-10-08T22:53:58.192Z
Updated: 2026-10-09T15:34:24.199Z
Reserved: 2026-08-24T23:36:03.109Z
Link: CVE-2026-78659
Updated: 2026-10-09T15:27:26.255Z
Status : Awaiting Analysis
Published: 2026-10-08T23:17:03.270
Modified: 2026-10-09T16:35:35.900
Link: CVE-2026-78659
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