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Response snapshot Oct 30, 2026, 19:11 UTC

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VulnerabilityCVE-2026-63913

Linux kernel: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number.

At a glance

Exploited
Not known
Severity
8.2 High (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-2026-63913 (opens a new tab)

What happened

In the Linux kernel, the following vulnerability has been resolved:

netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check

An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number.

Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction. The relevant code path assumes the RST is a response to an outgoing SYN, but does not validate packet direction or ensure that a matching SYN was actually sent in the opposite direction.

Continue reading

As a result, a crafted packet sequence consisting of a SYN followed by an invalid-sequence RST can prematurely terminate an active NAT entry. This makes connection teardown easier than intended.

So, tighten the state transition logic to ensure that RST-triggered CLOSE transitions only occur when the RST is a valid response to a previously observed SYN in the correct direction.

Scores and how they were measured

CVSS base severity

8.2

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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-2026-63913 (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 30). Linux kernel: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check (CVE-2026-63913). https://kevwire.com/record/CVE-2026-63913

MLA

"Linux kernel: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check (CVE-2026-63913)." KEVWire, 30 Oct. 2026, kevwire.com/record/CVE-2026-63913.

Chicago

KEVWire. "Linux kernel: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check (CVE-2026-63913)." Last modified October 30, 2026. https://kevwire.com/record/CVE-2026-63913.

Evidence summary (plain text)

Linux kernel: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check (Jul 19, 2026).
In the Linux kernel, the following vulnerability has been resolved:

netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check

An unintended behavior in the TCP conntrack state machine allows a
connection to be forced into the CLOSE state using an RST packet with an
invalid sequence number.

Specifically, after a SYN packet is observed, an RST with an invalid SEQ
can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of
whether the RST corresponds to the expected reply direction.
CVSS 8.2 (version 3.1; evidence as of Oct 30, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-63913).
Sources:
NVD CVE-2026-63913: https://nvd.nist.gov/vuln/detail/CVE-2026-63913
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-30T17:40:59.917Z&lastModEndDate=2026-10-30T19:10:56.758Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-30T17:10:58.916Z&lastModEndDate=2026-10-30T18:40:56.214Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-30T16:36:00.636Z&lastModEndDate=2026-10-30T18:10:56.487Z&resultsPerPage=500&startIndex=0
Record ID: CVE-2026-63913.
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 30, 2026, 19:10 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