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CVE-2020-27837

Published: 28 December 2020

A flaw was found in GDM in versions prior to 3.38.2.1. A race condition in the handling of session shutdown makes it possible to bypass the lock screen for a user that has autologin enabled, accessing their session without authentication. This is similar to CVE-2017-12164, but requires more difficult conditions to exploit.

Notes

AuthorNote
mdeslaur
unlikely scenario, requires autologin to be enabled and for a
session to crash but then still work. Setting priority to "low"

Priority

Low

Cvss 3 Severity Score

6.4

Score breakdown

Status

Package Release Status
gdm3
Launchpad, Ubuntu, Debian
bionic Not vulnerable

focal Needed

groovy Ignored
(end of life)
hirsute Ignored
(end of life)
impish Ignored
(end of life)
jammy Needed

kinetic Ignored
(end of life, was needed)
lunar Not vulnerable
(43.0-1ubuntu1)
mantic Not vulnerable
(43.0-1ubuntu1)
trusty Does not exist

upstream
Released (3.38.2.1-1)
xenial Not vulnerable

Patches:
upstream: https://gitlab.gnome.org/GNOME/gdm/-/commit/dcdbaaa04012541ad2813cf83559d91d52f208b9 (master)
upstream: https://gitlab.gnome.org/GNOME/gdm/-/commit/9b6d9b24a5f69674447c7bc9aacfab0988b914bd (3.38.2.1)

Severity score breakdown

Parameter Value
Base score 6.4
Attack vector Physical
Attack complexity High
Privileges required None
User interaction None
Scope Unchanged
Confidentiality High
Integrity impact High
Availability impact High
Vector CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H