tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction
Summary
| CVE | CVE-2026-64024 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-07-19 16:17:42 UTC |
| Updated | 2026-07-20 15:17:03 UTC |
| 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% |
Risk And Classification
Primary CVSS: v3.1 9.4 CRITICAL from 416baaa9-dc9f-4396-8d5f-8c081fb06d67
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
EPSS: 0.001660000 probability, percentile 0.061630000 (date 2026-07-20)
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | Secondary | 9.4 | CRITICAL | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H |
| 3.1 | CNA | DECLARED | 9.4 | CRITICAL | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
LowIntegrity
HighAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 e47f7060eaf60894e3e4d0e3c4fe6e1f2eacfbdd git | Not specified |
| CNA | Linux | Linux | affected 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 4affe063fa56c880cbea8d0bfded0bb80751579d git | Not specified |
| CNA | Linux | Linux | affected 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 1bbf0ced1d9db73ac7893c2187f3459288603e0d git | Not specified |
| CNA | Linux | Linux | affected 6.10 | Not specified |
| CNA | Linux | Linux | unaffected 6.10 semver | Not specified |
| CNA | Linux | Linux | unaffected 6.18.34 6.18.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.0.11 7.0.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.1 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/4affe063fa56c880cbea8d0bfded0bb80751579d | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/1bbf0ced1d9db73ac7893c2187f3459288603e0d | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/e47f7060eaf60894e3e4d0e3c4fe6e1f2eacfbdd | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.