Bug 1346016 (CVE-2016-4980)

Summary:	CVE-2016-4980 xguest insecure password creation
Product:	[Other] Security Response	Reporter:	Kurt Seifried <kseifried>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED WONTFIX	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	dkholia, dwalsh, lvrabec, mgrepl, mmalik, plautrba, sgrubb
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2016-07-28 05:00:03 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:	1346017
Bug Blocks:	1346019, 1349160

Description Kurt Seifried 2016-06-13 16:44:59 UTC

Kurt Seifried of Red Hat reports:

The xguest rpm creates a user and sets a password using the following rpm postinstall script:

head -1 /dev/urandom | passwd xguest --stdin > /dev/null

this can lead to insufficient randomness being used (in testing with head -n 1 /dev/urandom | wc -c it took an average of 10 attempts to get only 2 characters out). This password is required due to GDM requiring a password for automated passwordless logins at the console. 

A better method would be to use a tool such as openssl to get a guaranteed amount of entropy to create the password. 

Additionally this password needs to be unique per instance or install but this value is created at install-time and not during the first run. All container and image instances created would share the same password as this password is set at rpm install time, and each instance should recieve a unique password. 

This bug is being file because Product Security considers "first run problems" to be bugs with the source package and with the container or image only in the aggregate. This view is in collaboration with upstream Fedora. See: https://fedorahosted.org/fpc/ticket/506

The recommended resolution for services is to follow the "First-time Service Setup" pattern (see: https://fedoraproject.org/wiki/Packaging:Initial_Service_Setup ). Other packages may should use a runtime check and generation or similar procedure.

Comment 1 Kurt Seifried 2016-06-13 16:45:09 UTC

Acknowledgments:

Name: Kurt Seifried (Red Hat)

Comment 2 Kurt Seifried 2016-06-13 16:46:15 UTC

Created xguest tracking bugs for this issue:

Affects: fedora-all [bug 1346017]

Comment 3 Steve Grubb 2016-06-13 16:54:47 UTC

Probably head -c 24 (or some number) would fix it. The issue is that if the random string contains 0x0A, then head sees it as a new line and stops collecting random bytes.

Comment 4 Fedora Update System 2016-06-29 12:56:19 UTC

xguest-1.0.10-34.fc24 has been pushed to the Fedora 24 stable repository. If problems still persist, please make note of it in this bug report.

Comment 5 Fedora Update System 2016-06-29 17:22:59 UTC

xguest-1.0.10-33.fc23 has been pushed to the Fedora 23 stable repository. If problems still persist, please make note of it in this bug report.

Comment 6 Kurt Seifried 2016-07-15 18:05:50 UTC

(In reply to Steve Grubb from comment #3)
> Probably head -c 24 (or some number) would fix it. The issue is that if the
> random string contains 0x0A, then head sees it as a new line and stops
> collecting random bytes.

dd is much safer as you get a definite quantity of entropy.