--- id: CVE-2026-78663 title: >- The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered da… summary: >- The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered da… severity: critical cvss: 9.1 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H' cwe: - CWE-675 - 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: '2026-10-09T17:16:49.420' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-78663' references: - url: 'https://go.dev/cl/847187' label: security@golang.org - url: 'https://go.dev/cl/847310' label: security@golang.org - url: 'https://go.dev/issue/81743' 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-2026-6612' label: security@golang.org - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-78663.json - url: 'https://access.redhat.com/security/cve/CVE-2026-78663' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2548345' - url: 'https://www.cve.org/CVERecord?id=CVE-2026-78663' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-78663' - 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 - csaf - vex - red-hat - cve.org - score-dispute epss: 0.00622 epssPercentile: 0.49589 aliases: - GO-2026-6612 - BIT-golang-2026-78663 ecosystem: go scores: nvd: 9.1 vendor: 5.3 adp: 9.1 ingestedAt: '2026-10-09T00:19:50.975Z' ssvc: exploitation: none automatable: 'yes' technicalImpact: total timestamp: '2026-10-09T16:40:08.220862Z' --- ## Overview The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data. A malicious client can exploit this to bypass the configured connection-level flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still limited by the concurrent stream limit and stream-level flow control. ## Remediation Refer to the linked advisories for vendor-supplied fixes and affected version ranges. ## Package advisory (CVE-2026-78663) 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-2026-6612 ## Vendor advisories - **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-2026-78663.json) - **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) - **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)