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Fencer Vulns
critical 9.8

CVE-2018-20784 in the critical feed json

In the Linux kernel before 4.20.2, kernel/sched/fair.c mishandles leaf cfs_rq's, which allows attackers to cause a denial of service (infin…

published 2019-02-22 7 y ago modified 2026-06-17 4 mo ago also EUVD-2018-13327

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
4.2%
EPSS 4.2% chance of exploitation in 30 days, percentile 90%
public exploits
0
none known

Summary

In the Linux kernel before 4.20.2, kernel/sched/fair.c mishandles leaf cfs_rq's, which allows attackers to cause a denial of service (infinite loop in update_blocked_averages) or possibly have unspecified other impact by inducing a high load.

Patch / fix

  • linux linux_kernel 4.14.93, 4.19.15, 4.20.2
  • linux Debian 14, Debian 13, Debian 12 4.19.16-1

debian advisories DEBIAN-CVE-2018-20784

  • linux Ubuntu 16.04 LTS 4.4.0-170.199
  • linux Ubuntu 18.04 LTS 4.15.0-60.67
  • linux-aws Ubuntu 16.04 LTS 4.4.0-1099.110
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1047.49
  • linux-gcp Ubuntu 16.04 LTS 4.15.0-1041.43
  • linux-gcp Ubuntu 18.04 LTS 4.15.0-1042.45
  • linux-hwe Ubuntu 16.04 LTS 4.15.0-60.67~16.04.1
  • linux-hwe Ubuntu 18.04 LTS 5.0.0-23.24~18.04.1

ubuntu advisories UBUNTU-CVE-2018-20784

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-rt RHEL 8 4.18.0-80.7.1.rt9.153.el8_0
  • kernel-rt-kvm RHEL 8 4.18.0-80.7.1.rt9.153.el8_0
  • kernel-rt-core RHEL 8 4.18.0-80.7.1.rt9.153.el8_0
  • kernel-rt-modules RHEL 8 4.18.0-80.7.1.rt9.153.el8_0
  • kernel-rt-debug-kvm RHEL 8 4.18.0-80.7.1.rt9.153.el8_0
  • kernel-rt-debug-core RHEL 8 4.18.0-80.7.1.rt9.153.el8_0
  • kernel-rt-debug-modules RHEL 8 4.18.0-80.7.1.rt9.153.el8_0
  • kernel-rt-modules-extra RHEL 8 4.18.0-80.7.1.rt9.153.el8_0

red hat advisories RHSA-2019:1971RHSA-2019:1959

  • kernel-syms SLES 12 SP2-BCL 4.4.121-92.208.1
  • kernel-source SLES 12 SP2-BCL 4.4.121-92.208.1
  • kernel-default SLES 12 SP2-BCL 4.4.121-92.208.1
  • kernel-syms SLES 12 SP2-BCL 4.4.121-92.205.1
  • kernel-source SLES 12 SP2-BCL 4.4.121-92.205.1
  • kernel-default SLES 12 SP2-BCL 4.4.121-92.205.1
  • kernel-syms SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +3 more 4.4.180-94.164.2
  • kernel-source SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +3 more 4.4.180-94.164.2

suse advisories SUSE-SU-2023:3324-1SUSE-SU-2023:2805-1SUSE-SU-2022:2082-1SUSE-SU-2022:2077-1

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-2018-20784 updated cvss 5.9

kernel: infinite loop in update_blocked_averages() in kernel/sched/fair.c leading to denial of service

  • Red Hat Enterprise Linux 7 perf, kernel, kernel-alt, python-perf, kernel-kdump, kernel-tools, +3 more
    affected: no fix planned “Will not fix”
  • Red Hat CodeReady Linux Builder (v. 8) kernel-debuginfo-common-x86_64 4.18.0-80.7.1.el8_0, kernel-debuginfo-common-aarch64 4.18.0-80.7.1.el8_0, kernel-debuginfo-common-ppc64le 4.18.0-80.7.1.el8_0 Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-80.7.1.el8_0, kernel 4.18.0-80.7.1.el8_0, bpftool 4.18.0-80.7.1.el8_0, kernel-core 4.18.0-80.7.1.el8_0, kernel-tools 4.18.0-80.7.1.el8_0, python3-perf 4.18.0-80.7.1.el8_0, +15 more
    fixed: vendor fix RHSA-2019:1959
  • Red Hat Enterprise Linux Real Time (v. 8) kernel-rt 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-core 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-modules 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-debug-core 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-debug-modules 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-modules-extra 4.18.0-80.7.1.rt9.153.el8_0, +2 more Red Hat Enterprise Linux Real Time for NFV (v. 8) kernel-rt 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-kvm 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-core 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-modules 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-debug-kvm 4.18.0-80.7.1.rt9.153.el8_0, kernel-rt-debug-core 4.18.0-80.7.1.rt9.153.el8_0, +4 more
    fixed: vendor fix RHSA-2019:1971
  • 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 kernel, bpftool, kernel-rt, kernel-rt-kvm, kernel-rt-trace, kernel-rt-debug-kvm, +1 more Red Hat Enterprise MRG 2 kernel-rt, mrg-rt-release, kernel-rt-trace, kernel-rt-vanilla, kernel-rt-firmware
    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

4.17% chance of exploitation in the next 30 days, higher than 90% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

Classification

Weakness
  • CWE-835 Loop with Unreachable Exit Condition
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.