Bug 1154107

Summary:	CVE-2014-7300 gnome-shell: lockscreen bypass with printscreen key [rhel-7.1]
Product:	Red Hat Enterprise Linux 7	Reporter:	Florian Müllner <fmuellner>
Component:	gnome-shell	Assignee:	Florian Müllner <fmuellner>
Status:	CLOSED ERRATA	QA Contact:	Desktop QE <desktop-qa-list>
Severity:	low	Docs Contact:
Priority:	unspecified
Version:	7.0	CC:	fmuellner, mboisver, mclasen, moez.roy, rstrode, security-response-team, tpelka
Target Milestone:	rc	Keywords:	Security, SecurityTracking
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Release Note
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2015-03-05 13:22:04 UTC	Type:	Bug
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:
Bug Blocks:	1147917

Description Florian Müllner 2014-10-17 14:48:16 UTC

+++ This bug was initially created as a clone of Bug #1147917 +++

It was discovered [1] that PrtSc key is not disabled when the screen is locked.

Taking a bunch of screenshots at once bloats gnome-shell to the point
where it's pretty easy to get it targeted by the kernel's oom-killer.
This means that anyone with access to the keyboard of a locked GNOME
session can (briefly) disable the lockscreen, which lets them see and
interact with the running gnome session.

This might be fixed in gnome-shell 3.14.1, some patches available in the original bugreport [1].

[1]: https://bugzilla.gnome.org/show_bug.cgi?id=737456

--- Additional comment from Murray McAllister on 2014-10-02 22:17:43 EDT ---


Created gnome-shell tracking bugs for this issue:

Affects: fedora-all [bug 1149039]

--- Additional comment from Vasyl Kaigorodov on 2014-10-06 07:00:52 EDT ---

CVE-2014-7300 was assigned for:

"PrtSc is an unauthenticated request that's available to untrusted
parties. A series of requests can consume a large amount of memory.
The combination of this PrtSc behavior and the existence of the
oom-killer allows authentication bypass for command execution.
Therefore, the product must limit the aggregate memory consumption of
all active requests, and the lack of this limit is a vulnerability."

http://seclists.org/oss-sec/2014/q4/91

Comment 3 Michael Boisvert 2014-12-17 16:30:15 UTC

With gnome-shell-3.8.4-45.el7, I am seeing that PrntScrn is still enabled on the lock screen, but holding it down for 2+ minutes did not cause a crash and subsequent security breach. Is the fix that PrtScrn is disabled on the lock screen or something else?

Comment 4 Ray Strode [halfline] 2014-12-17 16:40:24 UTC

I believe the fix is to disable multiple concurrent screenshots at a time. So now it only allows one at a time so it can't overwhelm the system.

Comment 7 errata-xmlrpc 2015-03-05 13:22:04 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHSA-2015-0535.html

Comment 8 Florian Müllner 2015-05-20 15:17:57 UTC

(In reply to Ray Strode [halfline] from comment #4)
> I believe the fix is to disable multiple concurrent screenshots at a time.
> So now it only allows one at a time so it can't overwhelm the system.

That was indeed the original fix that went into 7.1. Upstream there was also an accompanying gnome-settings-daemon change that disabled screenshots altogether when locked, however I don't think it was backported to RHEL. The desktop rebase in 7.2 will bring it in though.