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Fencer Vulns
low 3.3

CVE-2021-38209 json

net/netfilter/nf_conntrack_standalone.c in the Linux kernel before 5.12.2 allows observation of changes in any net namespace because these…

published 2021-08-08 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-24667

cvss
3.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 20%
public exploits
0
none known

Summary

net/netfilter/nf_conntrack_standalone.c in the Linux kernel before 5.12.2 allows observation of changes in any net namespace because these changes are leaked into all other net namespaces. This is related to the NF_SYSCTL_CT_MAX, NF_SYSCTL_CT_EXPECT_MAX, and NF_SYSCTL_CT_BUCKETS sysctls.

Patch / fix

  • linux linux_kernel 5.12.2
  • linux Debian 14, Debian 13, Debian 12 5.10.38-1

debian advisories DEBIAN-CVE-2021-38209

  • linux-hwe-5.8 Ubuntu 20.04 LTS 5.8.0-59.66~20.04.1
  • linux-oem-5.10 Ubuntu 20.04 LTS 5.10.0-1029.30
  • linux-azure-5.8 Ubuntu 20.04 LTS 5.8.0-1036.38~20.04.1
  • linux-bluefield Ubuntu 20.04 LTS 5.4.0-1016.19

ubuntu advisories UBUNTU-CVE-2021-38209

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-default SLE Workstation Extension 15 SP3, SLE Module for Legacy 15 SP3, SLE Module for Basesystem 15 SP3 +3 more 5.3.18-59.24.1
  • kernel-default-base SLE Module for Basesystem 15 SP3, SLE Micro 5.1 5.3.18-59.24.1.18.12.1
  • kernel-64kb SLE Module for Basesystem 15 SP3 5.3.18-59.24.1
  • kernel-syms SLE Module for Development Tools 15 SP3 5.3.18-59.24.1
  • kernel-source SLE Module for Development Tools 15 SP3, SLE Module for Basesystem 15 SP3 5.3.18-59.24.1
  • kernel-preempt SLE Workstation Extension 15 SP3, SLE Module for Development Tools 15 SP3, SLE Module for Basesystem 15 SP3 5.3.18-59.24.1
  • kernel-zfcpdump SLE Module for Basesystem 15 SP3 5.3.18-59.24.1
  • kernel-obs-build SLE Module for Development Tools 15 SP3 5.3.18-59.24.1

suse advisories SUSE-SU-2021:3205-2SUSE-SU-2021:3205-1SUSE-SU-2021:3179-1

  • dtb-aarch64 openSUSE Leap 15.3 5.3.18-59.24.1
  • kernel-64kb openSUSE Leap 15.3 5.3.18-59.24.1
  • kernel-syms openSUSE Leap 15.3 5.3.18-59.24.1
  • kernel-obs-qa openSUSE Leap 15.3 5.3.18-59.24.1
  • kernel-source openSUSE Leap 15.3 5.3.18-59.24.1
  • kernel-default openSUSE Leap 15.3 5.3.18-59.24.1
  • kernel-preempt openSUSE Leap 15.3 5.3.18-59.24.1
  • kernel-kvmsmall openSUSE Leap 15.3 5.3.18-59.24.1

opensuse advisories openSUSE-SU-2021:3205-1openSUSE-SU-2021:3179-1

  • kernel CBL-Mariner 2.0 5.10.78.1-1

azure linux advisories AZL-6593

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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-2021-38209 updated cvss 3.3

kernel: net/netfilter/nf_conntrack_standalone.c allows observation of changes in any net namespace because these changes are leaked into all other net namespaces

  • Red Hat Enterprise Linux 5 kernel Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, kernel-alt, python-perf, kernel-kdump, kernel-tools, +3 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 kernel, bpftool, kernel-rt, kernel-rt-kvm, kernel-rt-trace, kernel-rt-debug-kvm, +1 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more
    not affected: vulnerable code not present

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

Exploit prediction

0.28% chance of exploitation in the next 30 days, higher than 20% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 3.3 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:P/I:N/A:N

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns 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.