CVE-2026-78659 HTTP/2 server memory exhaustion due to Trailer headers in net/http
A malicious client can cause memory exhaustion in Go HTTP/2 servers by sending excessive Trailer headers, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-78659?
CVE-2026-78659 is a high-severity denial of service vulnerability in golang.org/x/net/http2, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-405
Which versions are affected by CVE-2026-78659?
4 open source packages ship an affected version, including stdlib, golang and golang.org/x/net.
| Package | Affected | Fixed in |
|---|---|---|
stdlib Go | All versions | 1.26.9 |
stdlib Go | From 1.27.0-0 | 1.27.2 |
golang Bitnami | All versions | 1.26.9, 1.27.2 |
golang.org/x/net Go | All versions | 0.60.0 |
How do I fix CVE-2026-78659?
Upgrade stdlib to a fixed version for your release line: 1.26.9 or 1.27.2.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-78659 being exploited?
There is no known exploitation of CVE-2026-78659 in the wild and no public exploit code.
Sources
Also known as AZL-107021, AZL-107039, AZL-107069, AZL-107087, AZL-107114, AZL-107135 and 1100 more.