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Fencer Vulns
medium 5.1

CVE-2020-36557 json

A race condition in the Linux kernel before 5.6.2 between the VT_DISALLOCATE ioctl and closing/opening of ttys could lead to a use-after-fr…

published 2022-07-21 4 y ago modified 2026-06-17 4 mo ago also EUVD-2020-24033

cvss
5.1
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 10%
public exploits
0
none known

Summary

A race condition in the Linux kernel before 5.6.2 between the VT_DISALLOCATE ioctl and closing/opening of ttys could lead to a use-after-free.

Patch / fix

  • linux linux_kernel 5.6.2
  • linux Debian 14, Debian 13, Debian 12 5.5.17-1

debian advisories DEBIAN-CVE-2020-36557

  • linux Ubuntu 16.04 LTS 4.4.0-179.209
  • linux Ubuntu 18.04 LTS 4.15.0-99.100
  • linux-aws Ubuntu 16.04 LTS 4.4.0-1107.118
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1066.70
  • linux-gcp Ubuntu 16.04 LTS 4.15.0-1061.65
  • linux-hwe Ubuntu 16.04 LTS 4.15.0-99.100~16.04.1
  • linux-kvm Ubuntu 16.04 LTS 4.4.0-1071.78
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1059.60

ubuntu advisories UBUNTU-CVE-2020-36557

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 4.18.0-305.el8
  • perf RHEL 8 4.18.0-305.el8
  • bpftool RHEL 8 4.18.0-305.el8
  • kernel-core RHEL 8 4.18.0-305.el8
  • kernel-tools RHEL 8 4.18.0-305.el8
  • python3-perf RHEL 8 4.18.0-305.el8
  • kernel-modules RHEL 8 4.18.0-305.el8
  • kernel-zfcpdump RHEL 8 4.18.0-305.el8

red hat advisories RHSA-2021:1578

  • kernel-syms SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.12.14-95.108.1
  • kernel-source SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.12.14-95.108.1
  • kernel-default SLES for SAP 12 SP4, SLES 12 SP4-LTSS, SLE Live Patching 12 SP4 +3 more 4.12.14-95.108.1
  • kernel-rt SLE Real Time 12 SP5 4.12.14-10.97.1
  • kernel-syms-rt SLE Real Time 12 SP5 4.12.14-10.97.1
  • kernel-rt_debug SLE Real Time 12 SP5 4.12.14-10.97.1
  • kernel-source-rt SLE Real Time 12 SP5 4.12.14-10.97.1
  • kernel-rt SLE Micro 5.2, SLE Micro 5.1, Real Time Module 15 SP3 +1 more 5.3.18-150300.99.1

suse advisories SUSE-SU-2023:0416-1SUSE-SU-2022:4129-1SUSE-SU-2022:4027-1SUSE-SU-2022:3274-1SUSE-SU-2022:2910-1SUSE-SU-2022:2892-2

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-2020-36557 updated cvss 5.1

kernel: race condition between the VT_DISALLOCATE ioctl and closing/opening of ttys, causing a use-after-free in con_shutdown().

  • Red Hat Enterprise Linux 8 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +6 more
    affected: no fix available
  • Red Hat CodeReady Linux Builder (v. 8) perf 4.18.0-305.el8, kernel 4.18.0-305.el8, bpftool 4.18.0-305.el8, kernel-core 4.18.0-305.el8, kernel-tools 4.18.0-305.el8, python3-perf 4.18.0-305.el8, +15 more Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-305.el8, kernel 4.18.0-305.el8, bpftool 4.18.0-305.el8, kernel-core 4.18.0-305.el8, kernel-tools 4.18.0-305.el8, python3-perf 4.18.0-305.el8, +15 more
    fixed: vendor fix RHSA-2021:1578
  • Red Hat CodeReady Linux Builder (v. 8) kernel-headers 4.18.0-305.el8, kernel-cross-headers 4.18.0-305.el8 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 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more Red Hat Enterprise Linux BaseOS (v. 8) kernel-headers 4.18.0-305.el8, kernel-cross-headers 4.18.0-305.el8
    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

0.20% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.1 CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
  • CWE-416 Use After Free
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.