CVE-2026-78659
HTTP/2 server memory exhaustion due to Trailer headers in net/http
Published Oct 8, 2026 · corrected/updated Oct 16, 2026 · evidence confidence medium
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.
Grounded briefings
Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.
Executive
CVE-2026-78659 is a unknown public vulnerability record for this product. It is not currently listed in the CISA Known Exploited catalog. Check the linked vendor or CERT advisories for patch status. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.
System administrator
Identify whether this product is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: golang.org/x/net (0 → 0.60.0); stdlib (0 → 1.26.9); stdlib (1.27.0-0 → 1.27.2). Check the linked vendor or CERT advisories for patch status. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.
Security analyst
Signals on file: no CVSS/EPSS yet. It is not currently listed in the CISA Known Exploited catalog. Sources contributing to this record: cve_org, osv. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.
Exploitation and remediation
Exploitation evidence
Not listed as known exploited in CISA KEV. Not in the CISA KEV catalog.
Patch and remediation
No required-action text is stored yet. Use the vendor or CERT links in Sources for patch availability.
Safe detection guidance
Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.
Code
The project this record applies to. Exploit listings stay in References.
No public source repository is identified for this product.
Timeline
Detection, updates, and resolution for this record.
Oct 8, 2026 · OSV.dev
Detected
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 disproporti
Oct 16, 2026 · OSV.dev
Fix available
stdlib fixed in 1.26.9; stdlib fixed in 1.27.2; golang.org/x/net fixed in 0.60.0
Oct 16, 2026 · OSV.dev
Fix available
stdlib fixed in 1.26.9
Oct 16, 2026 · OSV.dev
Fix available
stdlib fixed in 1.27.2
Oct 16, 2026 · OSV.dev
Fix available
golang.org/x/net fixed in 0.60.0
Oct 16, 2026 · OSV.dev
Updated
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 disproporti
Affected
- Go golang.org/x/net0 → 0.60.0
- Go stdlib0 → 1.26.9
- Go stdlib1.27.0-0 → 1.27.2