Bug 1490417 (CVE-2017-12164)

Summary:	CVE-2017-12164 gdm: lock screen can be circumvented when autologin is set
Product:	[Other] Security Response	Reporter:	Cedric Buissart <cbuissar>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	alexl, caillon+fedoraproject, gnome-sig, john.j5live, mbarnes, rhughes, rstrode
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:	A flaw was discovered in the gdm where gdm greeter was no longer setting the ran_once boolean during autologin. If autologin was enable for a victim, an attacker could simply select 'login as another user' to unlock their screen.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2017-09-12 09:29:09 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:	1484033
Bug Blocks:	1488875

Description Cedric Buissart 2017-09-11 13:51:34 UTC

The gnome lock screen can be unlocked without needing a password. 

Steps to Reproduce:
1. Enable Automatic Login for your account
2. Reboot
3. Lock screen
4. Click on the log in as another user button below the password prompt.

Actual results:
The screen unlocks without a password being entered.

Expected results:
A selection of other accounts is shown.

Comment 1 Cedric Buissart 2017-09-12 08:53:00 UTC

This vulnerability is a side effect of upstream https://git.gnome.org/browse/gdm/commit/?id=ff98b28, in gdm-3.24.1.
This patch is not part of gdm as shipped in RHEL 7, 6 or 5. As such, RHEL is not affected by this vulnerability.

Comment 2 Cedric Buissart 2017-09-12 09:13:39 UTC

Acknowledgments:

Name: Tobias Guggenmos