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CVE-2021-23240

Publication date 12 January 2021

Last updated 24 July 2024

Ubuntu priority

Negligible

Why this priority?

Cvss 3 Severity Score

7.8 · High

Score breakdown

selinux_edit_copy_tfiles in sudoedit in Sudo before 1.9.5 allows a local unprivileged user to gain file ownership and escalate privileges by replacing a temporary file with a symlink to an arbitrary file target. This affects SELinux RBAC support in permissive mode. Machines without SELinux are not vulnerable.

Read the notes from the security team

Status

Package Ubuntu Release Status
sudo 24.10 oracular
Not affected
24.04 LTS noble
Not affected
23.10 mantic
Not affected
23.04 lunar
Not affected
22.10 kinetic
Not affected
22.04 LTS jammy
Not affected
21.10 impish
Not affected
21.04 hirsute Ignored end of life
20.10 groovy Ignored end of life
20.04 LTS focal
Needs evaluation
18.04 LTS bionic
Needs evaluation
16.04 LTS xenial Ignored
14.04 LTS trusty
Needs evaluation

Notes

sbeattie

selinux is not the default MAC in Ubuntu, though users can boot into it.

rodrigo-zaiden

fs.protected_symlinks is '1' by default in Ubuntu, and if not changed, can prevent this issue from being exploited. There are backports available for version 1.8 but not straightforward for 1.8.16 (xenial baseline). Some of the selinux specific code that needs to be patched was added later in time and it seems to me that the backports for 1.8 are based on 1.8.32. So, in xenial, a fix would be very intrusive and likely to introduce a regression. The reproducer in sudo.ws reference does not reproduce in xenial. The fact that the reproducer does not reproduce, that the kernel hardening fs.protected_symlinks is '1' by default (with no clear reason to be turned off to '0'), that there is a very low possibility to have Ubuntu running selinux without a working policy and, mainly, that the risky of regression is high, we are marking this CVE as ignored for xenial.

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package Patch details
sudo

Severity score breakdown

Parameter Value
Base score 7.8 · High
Attack vector Local
Attack complexity Low
Privileges required Low
User interaction None
Scope Unchanged
Confidentiality High
Integrity impact High
Availability impact High
Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H