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Fencer Vulns
medium 5.1

CVE-2020-16120 json

Unprivileged overlay + shiftfs read access

published 2021-02-10 5 y ago modified 2026-06-17 4 mo ago also EUVD-2020-8086

cvss
5.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 36%
public exploits
0
none known

Summary

Overlayfs did not properly perform permission checking when copying up files in an overlayfs and could be exploited from within a user namespace, if, for example, unprivileged user namespaces were allowed. It was possible to have a file not readable by an unprivileged user to be copied to a mountpoint controlled by the user, like a removable device. This was introduced in kernel version 4.19 by commit d1d04ef ("ovl: stack file ops"). This was fixed in kernel version 5.8 by commits 56230d9 ("ovl: verify permissions in ovl_path_open()"), 48bd024 ("ovl: switch to mounter creds in readdir") and 05acefb ("ovl: check permission to open real file"). Additionally, commits 130fdbc ("ovl: pass correct flags for opening real directory") and 292f902 ("ovl: call secutiry hook in ovl_real_ioctl()") in kernel 5.8 might also be desired or necessary. These additional commits introduced a regression in overlay mounts within user namespaces which prevented access to files with ownership outside of the user namespace. This regression was mitigated by subsequent commit b6650da ("ovl: do not fail because of O_NOATIMEi") in kernel 5.11.

Patch / fix

  • Linux kernel Linux kernel 5.11.0
  • linux Debian 14, Debian 13, Debian 12 5.8.7-1

debian advisories DEBIAN-CVE-2020-16120

  • linux Ubuntu 18.04 LTS 4.15.0-121.123
  • linux Ubuntu 20.04 LTS 5.4.0-51.56
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1086.91
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1028.29
  • linux-gcp Ubuntu 16.04 LTS 4.15.0-1086.98~16.04.1
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1028.29
  • linux-hwe Ubuntu 16.04 LTS 4.15.0-120.122~16.04.1
  • linux-hwe Ubuntu 18.04 LTS 5.3.0-68.63

ubuntu advisories UBUNTU-CVE-2020-16120

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 for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.12.14-95.65.1
  • kernel-source SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.12.14-95.65.1
  • kernel-default SLES for SAP 12 SP4, SLES 12 SP4-LTSS, SLE Live Patching 12 SP4 +3 more 4.12.14-95.65.1
  • kernel-syms SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.63.1
  • kernel-source SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.63.1
  • kernel-default SLES for SAP 15, SLES 15-LTSS, SLE Live Patching 15 +3 more 4.12.14-150.63.1
  • kernel-vanilla SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.63.1
  • kernel-obs-build SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.63.1

suse advisories SUSE-SU-2020:3544-1SUSE-SU-2020:3532-1SUSE-SU-2020:3522-1SUSE-SU-2020:3513-1SUSE-SU-2020:3512-1SUSE-SU-2020:3491-1

  • kernel-rt openSUSE Leap 15.2 5.3.18-lp152.3.5.1
  • kernel-syms-rt openSUSE Leap 15.2 5.3.18-lp152.3.5.1
  • kernel-rt_debug openSUSE Leap 15.2 5.3.18-lp152.3.5.1
  • kernel-source-rt openSUSE Leap 15.2 5.3.18-lp152.3.5.1
  • kernel-default-base openSUSE Leap 15.2 5.3.18-lp152.50.1.lp152.8.10.1
  • kernel-syms openSUSE Leap 15.2 5.3.18-lp152.50.1
  • kernel-obs-qa openSUSE Leap 15.2 5.3.18-lp152.50.1
  • kernel-source openSUSE Leap 15.2 5.3.18-lp152.50.1

opensuse advisories openSUSE-SU-2021:0242-1openSUSE-SU-2020:2112-1openSUSE-SU-2020:1906-1

  • kernel CBL-Mariner 2.0 5.10.78.1-1

azure linux advisories AZL-6522

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

  • linux Arch Linux 5.8.arch1-1

arch linux advisories AVG-1242

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-2020-16120 updated cvss 4.1

kernel: incorrect unprivileged overlayfs permission checking may lead to information disclosure

  • Red Hat Enterprise MRG 2 kernel
    affected: workaround, no fix planned “Will not fix”
  • 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, kernel-alt, python-perf, +9 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 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

0.42% chance of exploitation in the next 30 days, higher than 36% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.1 CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 3.1 4.4 CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:P/I:N/A:N

Affected products

  • Linux kernel Linux kernel

Classification

Weakness
  • CWE-266 Incorrect Privilege Assignment
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.