CVE-2026-78659: CWE-405: Asymmetric Resource Consumption (Amplification) in Go standard library net/http
Description
CVE-2026-78659 is an asymmetric resource consumption vulnerability in the Go standard library net/http package. It occurs when a malicious HTTP/2 client sends a "Trailer" header declaring a large number of fields, causing the server to allocate excessive memory by populating the Request.Trailer map. This bypasses the Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits. The issue does not affect HTTP/1 servers due to their different handling of headers and lack of multiplexing. No CVSS score is available for this vulnerability.
Affected software
Go standard library
net/http
Go standard library
net/http/internal/http2
golang.org/x/net
golang.org/x/net/http2
pkg:golang/net/http/internal/http2pkg:golang/golang.org/x/net/http2Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability arises from the way the Go net/http server handles "Trailer" headers sent by clients. For HTTP/2, the server uses the header values to populate the Request.Trailer map, which incurs memory overhead for each entry. A malicious client can exploit this by sending a Trailer header with many fields, causing disproportionate memory allocation and bypassing configured header limits. HTTP/1 servers are not affected because they do not multiplex requests over a single TCP connection and calculate header limits differently.
Potential Impact
A malicious HTTP/2 client can cause the server to consume excessive memory by sending a large number of Trailer header fields. This can lead to resource exhaustion, potentially degrading server performance or causing denial of service. The vulnerability does not apply to HTTP/1 servers.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, consider limiting exposure to untrusted HTTP/2 clients or implementing external rate limiting to mitigate potential resource exhaustion.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- Go
- Date Reserved
- 2026-08-24T23:36:03.109Z
- State
- PUBLISHED
Threat ID: 6ac821632cdf04f6564170d9
Added to database: 10/08/2026, 23:04:03 UTC
Last enriched: 10/08/2026, 23:19:35 UTC
Last updated: 10/08/2026, 23:19:35 UTC
Views: 7
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