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Fencer Intel
high 8.2

CVE-2026-63913 json

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

published 3mo ago modified 12d ago also EUVD-2026-45686

cvss
8.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.0%
EPSS 1.0% chance of exploitation in 30 days, percentile 62%
public exploits
0
none known

Summary

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.

Patch / fix

  • Linux Linux 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, 6.18.35, 7.0.12, 7.1
  • linux Debian 12 6.1.176-1
  • linux Debian 13 6.12.94-1
  • linux Debian 14 7.0.12-1

debian advisories DEBIAN-CVE-2026-63913

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 24.04 LTS 6.8.0-146.146
  • linux Ubuntu 26.04 LTS 7.0.0-28.28
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1066.69
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1009.9
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1070.78

ubuntu advisories UBUNTU-CVE-2026-63913

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 9 5.14.0-687.49.1.el9_8
  • rv RHEL 9 5.14.0-687.49.1.el9_8
  • perf RHEL 9 5.14.0-687.49.1.el9_8
  • rtla RHEL 9 5.14.0-687.49.1.el9_8
  • libperf RHEL 9 5.14.0-687.49.1.el9_8
  • kernel-rt RHEL 9 5.14.0-687.49.1.el9_8
  • kernel-64k RHEL 9 5.14.0-687.49.1.el9_8
  • kernel-core RHEL 9 5.14.0-687.49.1.el9_8

red hat advisories RHSA-2026:68570RHSA-2026:59737RHSA-2026:59821

  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.84.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.84.1
  • kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-default SLE Workstation Extension 15 SP7, SLE Module for Legacy 15 SP7, SLE Module for Basesystem 15 SP7 +2 more 6.4.0-150700.53.84.1
  • kernel-zfcpdump SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-obs-build SLE Module for Development Tools 15 SP7 6.4.0-150700.53.84.1
  • kernel-default-base SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1.150700.17.47.1

suse advisories SUSE-SU-2026:4706-1SUSE-SU-2026:4687-1SUSE-SU-2026:4640-1SUSE-SU-2026:24316-1SUSE-SU-2026:24315-1SUSE-SU-2026:24181-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.39.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.39.1

opensuse advisories openSUSE-SU-2026:22091-1

  • kernel AlmaLinux 9 5.14.0-687.49.1.el9_8
  • rv AlmaLinux 9 5.14.0-687.49.1.el9_8
  • perf AlmaLinux 9 5.14.0-687.49.1.el9_8
  • rtla AlmaLinux 9 5.14.0-687.49.1.el9_8
  • libperf AlmaLinux 9 5.14.0-687.49.1.el9_8
  • kernel-rt AlmaLinux 9 5.14.0-687.49.1.el9_8
  • kernel-64k AlmaLinux 9 5.14.0-687.49.1.el9_8
  • kernel-core AlmaLinux 9 5.14.0-687.49.1.el9_8

almalinux advisories ALSA-2026:68570ALSA-2026:59737ALSA-2026:59821

  • kernel Rocky Linux 9 5.14.0-687.49.1.el9_8
  • kernel-rt Rocky Linux 8 4.18.0-553.158.1.rt7.499.el8_10
  • kernel Rocky Linux 8 4.18.0-553.158.1.el8_10

rocky linux advisories RLSA-2026:68570RLSA-2026:59737RLSA-2026:59821

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-63913 updated cvss 7.0

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

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more Red Hat Enterprise Linux 10 kernel
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.49.1.el9_8, perf 5.14.0-687.49.1.el9_8, rtla 5.14.0-687.49.1.el9_8, python3-perf 5.14.0-687.49.1.el9_8, kernel-devel-matched 5.14.0-687.49.1.el9_8, kernel-64k-devel-matched 5.14.0-687.49.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:68570
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) rv 5.14.0-427.162.1.el9_4, perf 5.14.0-427.162.1.el9_4, rtla 5.14.0-427.162.1.el9_4, kernel-devel-matched 5.14.0-427.162.1.el9_4, kernel-64k-devel-matched 5.14.0-427.162.1.el9_4, kernel-debug-devel-matched 5.14.0-427.162.1.el9_4, +6 more
    fixed: vendor fix RHSA-2026:98047
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.158.1.el8_10, kernel 4.18.0-553.158.1.el8_10, bpftool 4.18.0-553.158.1.el8_10, kernel-core 4.18.0-553.158.1.el8_10, kernel-tools 4.18.0-553.158.1.el8_10, python3-perf 4.18.0-553.158.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:59821
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.49.1.el9_8, kernel-64k 5.14.0-687.49.1.el9_8, kernel-core 5.14.0-687.49.1.el9_8, kernel-tools 5.14.0-687.49.1.el9_8, kernel-modules 5.14.0-687.49.1.el9_8, kernel-64k-core 5.14.0-687.49.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:68570
  • Red Hat Enterprise Linux BaseOS E4S (v.9.4) bpftool 7.3.0-427.162.1.el9_4, kernel 5.14.0-427.162.1.el9_4, kernel-64k 5.14.0-427.162.1.el9_4, kernel-core 5.14.0-427.162.1.el9_4, kernel-tools 5.14.0-427.162.1.el9_4, python3-perf 5.14.0-427.162.1.el9_4, +28 more
    fixed: vendor fix RHSA-2026:98047
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.49.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.49.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.49.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.49.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.49.1.el9_8
    fixed: vendor fix RHSA-2026:68570
show 7 more
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.158.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.158.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.158.1.el8_10
    fixed: vendor fix RHSA-2026:59821
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-kvm 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-core 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-modules 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-debug-kvm 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-debug-core 4.18.0-553.158.1.rt7.499.el8_10, +4 more
    fixed: vendor fix RHSA-2026:59737
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.49.1.el9_8, kernel-rt-64k 5.14.0-687.49.1.el9_8, kernel-rt-core 5.14.0-687.49.1.el9_8, kernel-rt-modules 5.14.0-687.49.1.el9_8, kernel-rt-64k-core 5.14.0-687.49.1.el9_8, kernel-rt-debug-core 5.14.0-687.49.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:68570
  • Red Hat Enterprise Linux Real Time E4S (v.9.4) kernel-rt 5.14.0-427.162.1.el9_4, kernel-rt-core 5.14.0-427.162.1.el9_4, kernel-rt-modules 5.14.0-427.162.1.el9_4, kernel-rt-debug-core 5.14.0-427.162.1.el9_4, kernel-rt-modules-core 5.14.0-427.162.1.el9_4, kernel-rt-debug-modules 5.14.0-427.162.1.el9_4, +4 more
    fixed: vendor fix RHSA-2026:98047
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.49.1.el9_8, kernel-rt-core 5.14.0-687.49.1.el9_8, kernel-rt-modules 5.14.0-687.49.1.el9_8, kernel-rt-debug-core 5.14.0-687.49.1.el9_8, kernel-rt-modules-core 5.14.0-687.49.1.el9_8, kernel-rt-debug-modules 5.14.0-687.49.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:68570
  • Red Hat Enterprise Linux Real Time for NFV E4S (v.9.4) kernel-rt 5.14.0-427.162.1.el9_4, kernel-rt-kvm 5.14.0-427.162.1.el9_4, kernel-rt-core 5.14.0-427.162.1.el9_4, kernel-rt-modules 5.14.0-427.162.1.el9_4, kernel-rt-debug-kvm 5.14.0-427.162.1.el9_4, kernel-rt-debug-core 5.14.0-427.162.1.el9_4, +6 more
    fixed: vendor fix RHSA-2026:98047
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-core 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-modules 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-debug-core 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-debug-modules 4.18.0-553.158.1.rt7.499.el8_10, kernel-rt-modules-extra 4.18.0-553.158.1.rt7.499.el8_10, +2 more
    fixed: vendor fix RHSA-2026:59737

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
26d ago

Exploit prediction

0.97% chance of exploitation in the next 30 days, higher than 62% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-20 Improper Input Validation
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.