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Response snapshot Oct 29, 2026, 18:26 UTC

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VulnerabilityCVE-2026-64024

Linux kernel: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction

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.

At a glance

Exploited
Not known
Severity
9.4 Critical (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-64024 (opens a new tab)

What happened

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

Continue reading

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%

Scores and how they were measured

CVSS base severity

9.4

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2026-64024 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  4. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 29). Linux kernel: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction (CVE-2026-64024). https://kevwire.com/record/CVE-2026-64024

MLA

"Linux kernel: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction (CVE-2026-64024)." KEVWire, 29 Oct. 2026, kevwire.com/record/CVE-2026-64024.

Chicago

KEVWire. "Linux kernel: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction (CVE-2026-64024)." Last modified October 29, 2026. https://kevwire.com/record/CVE-2026-64024.

Evidence summary (plain text)

Linux kernel: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction (Jul 19, 2026).
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.
CVSS 9.4 (version 3.1; evidence as of Oct 29, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-64024).
Sources:
NVD CVE-2026-64024: https://nvd.nist.gov/vuln/detail/CVE-2026-64024
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-29T15:26:12.549Z&lastModEndDate=2026-10-29T16:55:56.354Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-29T14:55:58.555Z&lastModEndDate=2026-10-29T16:25:57.944Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-29T14:26:02.030Z&lastModEndDate=2026-10-29T15:55:56.439Z&resultsPerPage=500&startIndex=0
Record ID: CVE-2026-64024.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 16:55 UTC. Ingestion is not an independent editorial investigation.

NVD status: Analyzed. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

Record detail