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Fencer Vulns
medium 5.5

CVE-2021-47223 json

net: bridge: fix vlan tunnel dst null pointer dereference

published 2024-05-21 2 y ago modified 2026-06-17 4 mo ago also EUVD-2021-33871

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits
0
none known

Summary

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

net: bridge: fix vlan tunnel dst null pointer dereference

This patch fixes a tunnel_dst null pointer dereference due to lockless access in the tunnel egress path. When deleting a vlan tunnel the tunnel_dst pointer is set to NULL without waiting a grace period (i.e. while it's still usable) and packets egressing are dereferencing it without checking. Use READ/WRITE_ONCE to annotate the lockless use of tunnel_id, use RCU for accessing tunnel_dst and make sure it is read only once and checked in the egress path. The dst is already properly RCU protected so we don't need to do anything fancy than to make sure tunnel_id and tunnel_dst are read only once and checked in the egress path.

Patch / fix

  • Linux Linux 4.14.238, 4.19.196, 5.4.128, 5.10.46, 5.12.13, 5.13
  • linux Debian 14, Debian 13, Debian 12 5.10.46-1

debian advisories DEBIAN-CVE-2021-47223

  • linux Ubuntu 18.04 LTS 4.15.0-156.163
  • linux Ubuntu 20.04 LTS 5.4.0-81.91
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1111.118
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1055.58
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1051.55
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1099.101
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1045.47
  • linux-azure Ubuntu 20.04 LTS 5.4.0-1056.58

ubuntu advisories UBUNTU-CVE-2021-47223

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-syms SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 4.12.14-122.247.1
  • kernel-source SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 4.12.14-122.247.1
  • kernel-default SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS, SLE Live Patching 12 SP5 4.12.14-122.247.1
  • kgraft-patch-SLE12-SP5_Update_65 SLE Live Patching 12 SP5 1-8.3.1

suse advisories SUSE-SU-2025:0565-1

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-2021-47223 updated cvss 5.5

kernel: net: bridge: fix vlan tunnel dst null pointer dereference

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: no fix planned “Will not fix”

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
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

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.