What is CVE-2026-78659?

CVE-2026-78659 is a high-severity vulnerability in Golang.org/x/net Golang.org/x/net/http2, classified under Asymmetric Resource Consumption (Amplification). CVSS score: 7.5/10. Published 2026-10-08.

How severe is CVE-2026-78659?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Golang.org/x/net Golang.org/x/net/http2

CVE-2026-78659

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.

Published 2026-10-08 · last modified 2026-10-09.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Weakness classification (CWE)

CWE-405 — Asymmetric Resource Consumption (Amplification)

References

Frequently asked questions

What is CVE-2026-78659?: CVE-2026-78659 is a high-severity vulnerability in Golang.org/x/net Golang.org/x/net/http2, classified under Asymmetric Resource Consumption (Amplification). CVSS score: 7.5/10. Published 2026-10-08.
How severe is CVE-2026-78659?: High severity. CVSS v3 base score is 7.5 out of 10.