Attacker Value
Unknown
(0 users assessed)
Exploitability
Unknown
(0 users assessed)
User Interaction
None
Privileges Required
High
Attack Vector
Local
0

CVE-2020-16120

Disclosure Date: October 13, 2020
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Description

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.

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CVSS V3 Severity and Metrics
Base Score:
4.4 Medium
Impact Score:
3.6
Exploitability Score:
0.8
Vector:
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N
Attack Vector (AV):
Local
Attack Complexity (AC):
Low
Privileges Required (PR):
High
User Interaction (UI):
None
Scope (S):
Unchanged
Confidentiality (C):
High
Integrity (I):
None
Availability (A):
None

General Information

Vendors

  • canonical,
  • linux

Products

  • linux kernel,
  • ubuntu linux 14.04,
  • ubuntu linux 16.04,
  • ubuntu linux 18.04,
  • ubuntu linux 20.04
Technical Analysis