Bug 1906812 (CVE-2020-27837)

Summary:	CVE-2020-27837 gdm: lock screen bypass when autologin is set
Product:	[Other] Security Response	Reporter:	Guilherme de Almeida Suckevicz <gsuckevi>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED WONTFIX	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	caillon+fedoraproject, gnome-sig, hdegoede, mclasen, normand, philip.wyett, rhughes, rstrode, security-response-team
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	gdm 3.38.2.1	Doc Type:	If docs needed, set a value
Doc Text:	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.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2020-12-21 19:31:05 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1908276
Bug Blocks:	1906515

Description Guilherme de Almeida Suckevicz 2020-12-11 13:30:26 UTC

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.

Reference:
https://gitlab.gnome.org/GNOME/gdm/-/issues/660

Comment 1 Riccardo Schirone 2020-12-16 09:59:30 UTC

Created gdm tracking bugs for this issue:

Affects: fedora-all [bug 1908276]

Comment 2 Riccardo Schirone 2020-12-16 11:04:06 UTC

Upstream patch:
https://gitlab.gnome.org/GNOME/gdm/-/commit/dcdbaaa04012541ad2813cf83559d91d52f208b9

Comment 4 Riccardo Schirone 2020-12-21 14:19:55 UTC

Low Impact assigned to this flaw due to multiple requirements being necessary:
1) automatic login needs to be enabled. This is usually not used in configurations that require high security
2) the session needs to crash once at startup, but then it should work well after that
3) it requires losing a race condition that's hard to lose without a PostSession script being installed

Comment 6 Product Security DevOps Team 2020-12-21 19:31:05 UTC

This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2020-27837