--- id: CVE-2026-64024 title: |- In the Linux kernel, the following vulnerability has been resolved: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction Blamed commit moved the TIME_WAIT-derived ISN from the skb control block to a per-CPU variable, assuming… summary: |- In the Linux kernel, the following vulnerability has been resolved: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction Blamed commit moved the TIME_WAIT-derived ISN from the skb control block to a per-CPU variable, assuming… severity: critical cvss: 9.4 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H' cwe: - CWE-401 - CWE-342 vendor: linux product: linux_kernel affected: - 'linux_kernel >= 6.10, < 6.18.34' - 'linux_kernel >= 6.19, < 7.0.11' - linux_kernel = 7.1 patched: - linux_kernel 7.0.11 published: '2026-07-19' updated: '2026-10-13' sourceUpdated: '2026-10-13T15:00:30.167' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64024' references: - url: 'https://git.kernel.org/stable/c/1bbf0ced1d9db73ac7893c2187f3459288603e0d' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/4affe063fa56c880cbea8d0bfded0bb80751579d' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/e47f7060eaf60894e3e4d0e3c4fe6e1f2eacfbdd' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64024.json - url: 'https://access.redhat.com/security/cve/CVE-2026-64024' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2502333' - url: 'https://www.cve.org/CVERecord?id=CVE-2026-64024' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64024' - url: >- https://lore.kernel.org/linux-cve-announce/2026071902-CVE-2026-64024-8c76@gregkh/T - url: 'https://access.redhat.com/errata/RHSA-2026:86033' - url: 'https://git.kernel.org/stable/c/8bb6aa419b142dcc2680177ecc39c4c38db7fc16' - url: 'https://access.redhat.com/errata/RHSA-2026:76738' tags: - nvd - cve.org - csaf - vex - red-hat - score-dispute epss: 0.00308 epssPercentile: 0.23441 ingestedAt: '2026-10-13T15:33:40.025Z' ssvc: exploitation: none automatable: 'yes' technicalImpact: partial timestamp: '2026-10-16T15:35:24.819208Z' scores: nvd: 9.4 vendor: 7 cna: 9.4 --- ## Overview In the Linux kernel, the following vulnerability has been resolved: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction Blamed commit moved the TIME_WAIT-derived ISN from the skb control block to a per-CPU variable, assuming the value would always be consumed by tcp_conn_request() for the same packet that wrote it. That assumption is violated by multiple drop paths between the producer (__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer (tcp_conn_request()): - min_ttl / min_hopcount check - xfrm policy check - tcp_inbound_hash() MD5/AO mismatch - tcp_filter() eBPF/SO_ATTACH_FILTER drop - th->syn && th->fin discard in tcp_rcv_state_process() TCP_LISTEN - psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv() - tcp_checksum_complete() in tcp_v{4,6}_do_rcv() - tcp_v{4,6}_cookie_check() returning NULL When a packet is dropped on any of these paths, tcp_tw_isn is left set. The next SYN processed on the same CPU then consumes the non zero value in tcp_conn_request(), receiving a potentially predictable ISN. This patch moves back tcp_tw_isn to skb->cb[], getting rid of the per-cpu variable. Note that tcp_v{4,6}_fill_cb() do not set it. Very litle impact on overall code size/complexity: $ scripts/bloat-o-meter -t vmlinux.old vmlinux.new add/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7) Function old new delta tcp_v6_rcv 3038 3042 +4 tcp_v4_rcv 3035 3039 +4 tcp_conn_request 2938 2923 -15 Total: Before=24436060, After=24436053, chg -0.00% ## Affected - `linux_kernel >= 6.10, < 6.18.34` - `linux_kernel >= 6.19, < 7.0.11` - `linux_kernel = 7.1` ## Remediation Upgrade past the affected range: - `linux_kernel 7.0.11` ## Vendor advisories - **RHSA-2026:86033** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux BaseOS (v. 9), Red Hat Enterprise Linux CodeReady Linux Builder (v. 9), Red Hat Enterprise Linux Real Time for NFV (v. 9), Red Hat Enterprise Linux Real Time (v. 9) · released 2026-10-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:86033) - **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 9 · updated 2026-10-26 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64024.json) - **RHSA-2026:76738** · Red Hat · fixed in: 10Base-SMTV, Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux BaseOS (v. 10), Red Hat Enterprise Linux CodeReady Linux Builder (v. 10), Red Hat Enterprise Linux Hidden (v. 10), Red Hat Enterprise Linux Real Time for NFV (v. 10), … · released 2026-10-08 · [advisory](https://access.redhat.com/errata/RHSA-2026:76738)