--- id: CVE-2026-78659 title: >- 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 summary: >- 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 HTT… severity: high cvss: 7.5 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H' cwe: - CWE-405 - CWE-770 vendor: stdlib product: stdlib affected: - stdlib < 1.26.9 - 'stdlib >= 1.27.0-0, < 1.27.2' - golang.org/x/net < 0.60.0 patched: - stdlib 1.26.9 - stdlib 1.27.2 - golang.org/x/net 0.60.0 published: '2026-10-08' updated: '2026-10-09' sourceUpdated: '2026-10-09T16:35:35.900' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-78659' references: - url: 'https://go.dev/cl/847185' label: security@golang.org - url: 'https://go.dev/cl/847314' label: security@golang.org - url: 'https://go.dev/issue/81857' label: security@golang.org - url: 'https://groups.google.com/g/golang-announce/c/U2fTuyDJznI' label: security@golang.org - url: 'https://groups.google.com/g/golang-announce/c/ZPwCyRUuGBs' label: security@golang.org - url: 'https://pkg.go.dev/vuln/GO-2026-6603' label: security@golang.org - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-78659.json - url: 'https://access.redhat.com/security/cve/CVE-2026-78659' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2548339' - url: 'https://www.cve.org/CVERecord?id=CVE-2026-78659' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-78659' - url: 'https://access.redhat.com/errata/RHSA-2026:87040' - url: 'https://access.redhat.com/errata/RHSA-2026:86093' - url: 'https://access.redhat.com/errata/RHSA-2026:86203' - url: 'https://access.redhat.com/errata/RHSA-2026:87246' - url: 'https://access.redhat.com/errata/RHSA-2026:87041' - url: 'https://access.redhat.com/errata/RHSA-2026:87042' - url: 'https://access.redhat.com/errata/RHSA-2026:87043' - url: 'https://access.redhat.com/errata/RHSA-2026:86196' - url: 'https://access.redhat.com/errata/RHSA-2026:87245' tags: - nvd - osv - go - cve.org - csaf - vex - red-hat aliases: - GO-2026-6603 - BIT-golang-2026-78659 ecosystem: go ingestedAt: '2026-10-09T00:19:50.975Z' epss: 0.00627 epssPercentile: 0.50197 ssvc: exploitation: none automatable: 'yes' technicalImpact: partial timestamp: '2026-10-09T15:27:33.510545Z' --- ## Overview 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. ## Remediation Refer to the linked advisories for vendor-supplied fixes and affected version ranges. ## Package advisory (CVE-2026-78659) Affected packages: - `stdlib < 1.26.9` - `stdlib >= 1.27.0-0, < 1.27.2` - `golang.org/x/net < 0.60.0` Patched in: - `stdlib 1.26.9` - `stdlib 1.27.2` - `golang.org/x/net 0.60.0` Source: https://osv.dev/vulnerability/GO-2026-6603 ## Vendor advisories - **RHSA-2026:87040** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream EUS (v. 10.0) · released 2026-10-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:87040) - **RHSA-2026:86093** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 10) · released 2026-10-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:86093) - **RHSA-2026:86203** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 8) · released 2026-10-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:86203) - **RHSA-2026:87246** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream AUS (v.8.6), Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.6) · released 2026-10-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:87246) - **RHSA-2026:87041** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream E4S (v.9.2) · released 2026-10-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:87041) - **RHSA-2026:87042** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream E4S (v.9.4) · released 2026-10-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:87042) - **RHSA-2026:87043** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream EUS (v.9.6) · released 2026-10-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:87043) - **RHSA-2026:86196** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9) · released 2026-10-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:86196) - **Red Hat VEX** · Moderate · affected: OpenShift Developer Tools and Services, OpenShift Pipelines, OpenShift Serverless, OpenShift Service Mesh 3, Red Hat Ansible Automation Platform 2, Red Hat Ceph Storage 7, … · no fix planned: OpenShift Developer Tools and Services, Red Hat Ansible Automation Platform 2, Red Hat OpenStack Platform 16.2, Red Hat OpenStack Platform 17.1, … · updated 2026-10-23 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-78659.json) - **RHSA-2026:87245** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream E4S (v.8.8), Red Hat Enterprise Linux AppStream TUS (v.8.8) · released 2026-10-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:87245)