Bug 1638570

Summary:	xorg-x11-server: Format string vulnerability in os/log.c:LogFilePrep() allows for memory disclosure and crash
Product:	[Other] Security Response	Reporter:	Sam Fowler <sfowler>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED WONTFIX	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	ajax, bskeggs, caillon+fedoraproject, jglisse, john.j5live, narendra, ofourdan, rhughes, rstrode, sandmann, security-response-team, sfowler, xgl-maint
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
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Last Closed:	2018-10-26 07:03:20 UTC	Type:	---
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Documentation:	---	CRM:
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	1638572

Description Sam Fowler 2018-10-11 23:55:10 UTC

The X.org X11 server has a format string vulnerability in the os/log.c:LogFilePrep() function. A local user can exploit this by executing the Xorg binary with crafted arguments to  read arbitrary memory and cause a crash.

Comment 1 Sam Fowler 2018-10-11 23:55:13 UTC

Acknowledgments:

Name: Narendra Shinde

Comment 4 Tomas Hoger 2018-10-25 14:42:51 UTC

Upstream is currently not fixing this issue in LogFilePrep(), as the file name passed to the function is expected to optionally contain format specifier %s.  The following comment-only change was made to explicitly note this expectation:

https://gitlab.freedesktop.org/xorg/xserver/commit/da15c7413916f754708c62c2089265528cd661e2

With the fix for CVE-2018-14665 (bug 1637761) applied, Xorg no longer allows -logfile option to be specified when running with elevated privileges, preventing exploitation of this flaw.  The root user would still be able to trigger crash or memory disclosure using this bug, but that does not cross any trust boundary and hence has not security impact.

Comment 5 Tomas Hoger 2018-10-26 06:58:06 UTC

Public now via a blog post from the original reporter, primarily written for CVE-2018-14665:

https://www.securepatterns.com/2018/10/cve-2018-14665-xorg-x-server.html

Comment 6 Tomas Hoger 2018-10-26 07:03:20 UTC

As explained in comment 4 above, this has no security impact after the fix for CVE-2018-14665 is applied, and hence is not planned to be addressed as a security flaw.