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Fencer Vulns
high 7.4

CVE-2021-20322 json

A flaw in the processing of received ICMP errors (ICMP fragment needed and ICMP redirect) in the Linux kernel functionality was found to al…

published 2022-02-18 4 y ago modified 2026-07-30 3 mo ago also EUVD-2021-7746

cvss
7.4
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
6.9%
EPSS 6.9% chance of exploitation in 30 days, percentile 94%
public exploits
0
none known

Summary

A flaw in the processing of received ICMP errors (ICMP fragment needed and ICMP redirect) in the Linux kernel functionality was found to allow the ability to quickly scan open UDP ports. This flaw allows an off-path remote user to effectively bypass the source port UDP randomization. The highest threat from this vulnerability is to confidentiality and possibly integrity, because software that relies on UDP source port randomization are indirectly affected as well.

Patch / fix

  • n/a kernel 4.19.215, 5.4.146, 5.10.65, 5.13.17, 5.14.4
  • linux Debian 14, Debian 13, Debian 12 5.14.6-1

debian advisories DEBIAN-CVE-2021-20322

  • linux Ubuntu 18.04 LTS 4.15.0-167.175
  • linux Ubuntu 20.04 LTS 5.4.0-92.103
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1119.127
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1061.64
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1059.63
  • linux-gke Ubuntu 20.04 LTS 5.4.0-1057.60
  • linux-ibm Ubuntu 20.04 LTS 5.4.0-1010.11
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1106.108

ubuntu advisories UBUNTU-CVE-2021-20322

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 8 4.18.0-372.9.1.el8
  • perf RHEL 8 4.18.0-372.9.1.el8
  • bpftool RHEL 8 4.18.0-372.9.1.el8
  • kernel-core RHEL 8 4.18.0-372.9.1.el8
  • kernel-tools RHEL 8 4.18.0-372.9.1.el8
  • python3-perf RHEL 8 4.18.0-372.9.1.el8
  • kernel-modules RHEL 8 4.18.0-372.9.1.el8
  • kernel-zfcpdump RHEL 8 4.18.0-372.9.1.el8

red hat advisories RHSA-2022:1988RHSA-2022:4829RHSA-2022:4835RHSA-2022:1975

  • kernel-rt SLE Real Time 12 SP5 4.12.14-10.70.2
  • kernel-syms-rt SLE Real Time 12 SP5 4.12.14-10.70.2
  • kernel-rt_debug SLE Real Time 12 SP5 4.12.14-10.70.2
  • kernel-source-rt SLE Real Time 12 SP5 4.12.14-10.70.2
  • kernel-rt SLE Micro 5.1, Real Time Module 15 SP3 5.3.18-65.2
  • kernel-syms-rt Real Time Module 15 SP3 5.3.18-65.1
  • kernel-rt_debug Real Time Module 15 SP3 5.3.18-65.2
  • kernel-source-rt Real Time Module 15 SP3 5.3.18-65.2

suse advisories SUSE-SU-2021:4099-1SUSE-SU-2021:4090-1SUSE-SU-2021:4075-1SUSE-SU-2021:4057-1SUSE-SU-2021:4038-1SUSE-SU-2021:4021-1

  • dtb-aarch64 openSUSE Leap 15.3 5.3.18-59.37.1
  • kernel-64kb openSUSE Leap 15.3 5.3.18-59.37.2
  • kernel-syms openSUSE Leap 15.3 5.3.18-59.37.1
  • kernel-obs-qa openSUSE Leap 15.3 5.3.18-59.37.1
  • kernel-source openSUSE Leap 15.3 5.3.18-59.37.2
  • kernel-default openSUSE Leap 15.3 5.3.18-59.37.2
  • kernel-preempt openSUSE Leap 15.3 5.3.18-59.37.2
  • kernel-kvmsmall openSUSE Leap 15.3 5.3.18-59.37.2

opensuse advisories openSUSE-SU-2021:3941-1openSUSE-SU-2021:3876-1openSUSE-SU-2021:3806-1openSUSE-SU-2021:1501-1

  • kernel AlmaLinux 8 4.18.0-372.9.1.el8
  • perf AlmaLinux 8 4.18.0-372.9.1.el8
  • bpftool AlmaLinux 8 4.18.0-372.9.1.el8
  • kernel-core AlmaLinux 8 4.18.0-372.9.1.el8
  • kernel-tools AlmaLinux 8 4.18.0-372.9.1.el8
  • python3-perf AlmaLinux 8 4.18.0-372.9.1.el8
  • kernel-modules AlmaLinux 8 4.18.0-372.9.1.el8
  • kernel-debug-core AlmaLinux 8 4.18.0-372.9.1.el8

almalinux advisories ALSA-2022:1988

  • kernel Rocky Linux 8 4.18.0-372.9.1.el8
  • kernel-rt Rocky Linux 8 4.18.0-372.9.1.rt7.166.el8

rocky linux advisories RLSA-2022:1988RLSA-2022:1975

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-2021-20322 updated cvss 7.4

kernel: new DNS Cache Poisoning Attack based on ICMP fragment needed packets replies

  • 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, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-372.9.1.el8, kernel 4.18.0-372.9.1.el8, bpftool 4.18.0-372.9.1.el8, kernel-core 4.18.0-372.9.1.el8, kernel-tools 4.18.0-372.9.1.el8, python3-perf 4.18.0-372.9.1.el8, +15 more
    fixed: vendor fix RHSA-2022:1988
  • Red Hat Enterprise Linux BaseOS EUS (v.8.4) perf 4.18.0-305.49.1.el8_4, kernel 4.18.0-305.49.1.el8_4, bpftool 4.18.0-305.49.1.el8_4, kernel-core 4.18.0-305.49.1.el8_4, kernel-tools 4.18.0-305.49.1.el8_4, python3-perf 4.18.0-305.49.1.el8_4, +15 more
    fixed: vendor fix RHSA-2022:4829
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-372.9.1.el8, kernel-debuginfo-common-aarch64 4.18.0-372.9.1.el8, kernel-debuginfo-common-ppc64le 4.18.0-372.9.1.el8
    fixed: vendor fix RHSA-2022:1988
  • Red Hat Enterprise Linux CRB EUS (v.8.4) kernel-debuginfo-common-x86_64 4.18.0-305.49.1.el8_4, kernel-debuginfo-common-aarch64 4.18.0-305.49.1.el8_4, kernel-debuginfo-common-ppc64le 4.18.0-305.49.1.el8_4
    fixed: vendor fix RHSA-2022:4829
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-372.9.1.rt7.166.el8, kernel-rt-kvm 4.18.0-372.9.1.rt7.166.el8, kernel-rt-core 4.18.0-372.9.1.rt7.166.el8, kernel-rt-modules 4.18.0-372.9.1.rt7.166.el8, kernel-rt-debug-kvm 4.18.0-372.9.1.rt7.166.el8, kernel-rt-debug-core 4.18.0-372.9.1.rt7.166.el8, +4 more
    fixed: vendor fix RHSA-2022:1975
  • Red Hat Enterprise Linux NFV EUS (v.8.4) kernel-rt 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-kvm 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-core 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-modules 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-debug-kvm 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-debug-core 4.18.0-305.49.1.rt7.121.el8_4, +4 more
    fixed: vendor fix RHSA-2022:4835
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-372.9.1.rt7.166.el8, kernel-rt-core 4.18.0-372.9.1.rt7.166.el8, kernel-rt-modules 4.18.0-372.9.1.rt7.166.el8, kernel-rt-debug-core 4.18.0-372.9.1.rt7.166.el8, kernel-rt-debug-modules 4.18.0-372.9.1.rt7.166.el8, kernel-rt-modules-extra 4.18.0-372.9.1.rt7.166.el8, +2 more
    fixed: vendor fix RHSA-2022:1975
show 2 more
  • Red Hat Enterprise Linux RT EUS (v.8.4) kernel-rt 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-core 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-modules 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-debug-core 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-debug-modules 4.18.0-305.49.1.rt7.121.el8_4, kernel-rt-modules-extra 4.18.0-305.49.1.rt7.121.el8_4, +2 more
    fixed: vendor fix RHSA-2022:4835
  • 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

6.90% chance of exploitation in the next 30 days, higher than 94% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD 2.0 5.8 AV:N/AC:M/Au:N/C:P/I:P/A:N

Affected products

  • n/a kernel

Classification

Weakness
  • CWE-330 Use of Insufficiently Random Values
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.