CVE-2026-64024
Full vulnerability record from the local CVENow database.
Description
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%
View original CVE JSON
{
"id": "CVE-2026-64024",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2026-07-19T16:17:42.413",
"lastModified": "2026-10-29T15:55:29.880",
"vulnStatus": "Analyzed",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction\n\nBlamed commit moved the TIME_WAIT-derived ISN from the skb control\nblock to a per-CPU variable, assuming the value would always be consumed\nby tcp_conn_request() for the same packet that wrote it. That assumption\nis violated by multiple drop paths between the producer\n(__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer\n(tcp_conn_request()):\n\n - min_ttl / min_hopcount check\n - xfrm policy check\n - tcp_inbound_hash() MD5/AO mismatch\n - tcp_filter() eBPF/SO_ATTACH_FILTER drop\n - th->syn && th->fin discard in tcp_rcv_state_process() TCP_LISTEN\n - psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv()\n - tcp_checksum_complete() in tcp_v{4,6}_do_rcv()\n - tcp_v{4,6}_cookie_check() returning NULL\n\nWhen a packet is dropped on any of these paths, tcp_tw_isn is left set.\n\nThe next SYN processed on the same CPU then consumes the non zero value in\ntcp_conn_request(), receiving a potentially predictable ISN.\n\nThis patch moves back tcp_tw_isn to skb->cb[], getting rid of the per-cpu\nvariable.\n\nNote that tcp_v{4,6}_fill_cb() do not set it.\n\nVery litle impact on overall code size/complexity:\n\n$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new\nadd/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7)\nFunction old new delta\ntcp_v6_rcv 3038 3042 +4\ntcp_v4_rcv 3035 3039 +4\ntcp_conn_request 2938 2923 -15\nTotal: Before=24436060, After=24436053, chg -0.00%"
}
],
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"affectedData": [
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"programFiles": [
"include/net/tcp.h",
"net/ipv4/tcp.c",
"net/ipv4/tcp_input.c",
"net/ipv4/tcp_ipv4.c",
"net/ipv6/tcp_ipv6.c"
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"net/ipv4/tcp_input.c",
"net/ipv4/tcp_ipv4.c",
"net/ipv6/tcp_ipv6.c"
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{
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"lessThanOrEqual": "6.18.*",
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{
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"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H",
"baseScore": 9.4,
"baseSeverity": "CRITICAL",
"attackVector": "NETWORK",
"attackComplexity": "LOW",
"privilegesRequired": "NONE",
"userInteraction": "NONE",
"scope": "UNCHANGED",
"confidentialityImpact": "LOW",
"integrityImpact": "HIGH",
"availabilityImpact": "HIGH"
},
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"impactScore": 5.5
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"timestamp": "2026-10-16T15:35:24.819208Z",
"id": "CVE-2026-64024",
"options": [
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},
{
"automatable": "yes"
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"role": "CISA Coordinator",
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"weaknesses": [
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"source": "[email protected]",
"type": "Primary",
"description": [
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"lang": "en",
"value": "CWE-401"
}
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{
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}
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