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Vulnerabilities

Vulnerability · CVE-2026-63913

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 uninten…

Published Jul 19, 2026 · catalog updated Oct 30, 2026 · linux kernel

Last checked Oct 31, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-63913. EPSS is 0.97%. Act only if a listed version of linux kernel is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High8.2
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.97%
Remediation
Version ranges on file
Affected products
cpe linux/linux kernel

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. 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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe linux/linux kernel7.1
  • cpe linux/linux kernel< 5.10.259
  • cpe linux/linux kernel< 5.15.210
  • cpe linux/linux kernel< 6.1.176
  • cpe linux/linux kernel< 6.12.93
  • cpe linux/linux kernel< 6.18.35
  • cpe linux/linux kernel< 6.6.143
  • cpe linux/linux kernel< 7.0.12

How to fix CVE-2026-63913

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-63913. EPSS is 0.97%. Act only if a listed version of linux kernel is installed.

Which versions are affected?

Compare what you have installed with linux/linux kernel 7.1; linux/linux kernel < 5.10.259; linux/linux kernel < 5.15.210; linux/linux kernel < 6.1.176. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-20: Improper Input Validation. EPSS 0.97%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 26, 2026 · BSI CERT-Bund

    Detected

    CVE-2026-63913 is listed by Linux Kernel: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff.

  2. Oct 30, 2026 · NIST NVD

    Updated

    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 t

Sources

  • BSI CERT-BundGovernment advisoryCVE-2026-63913

    Linux Kernel: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff

    wid.cert-bund.de
  • CVE.orgVulnerability recordCVE-2026-63913

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-63913

    30-day exploitation probability 0.97%

    first.org
  • NIST NVDVulnerability recordCVE-2026-63913

    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

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 29, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • NIST NVDOct 31, 2026
  • FIRST EPSSOct 29, 2026
  • CVE.orgOct 27, 2026
  • BSI CERT-BundOct 27, 2026