Bug 1623242 (CVE-2018-14600)

Summary:	CVE-2018-14600 libX11: Out of Bounds write in XListExtensions in ListExt.c
Product:	[Other] Security Response	Reporter:	Laura Pardo <lpardo>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED ERRATA	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	abhgupta, ajax, alanm, alexl, caillon+fedoraproject, dbaker, jglisse, john.j5live, jokerman, peter.hutterer, rhughes, rschiron, rstrode, sandmann, shivrao, slawomir, sthangav, trankin
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	libX11 1.6.6	Doc Type:	If docs needed, set a value
Doc Text:	An out of bounds write, limited to NULL bytes, was discovered in libX11 in functions XListExtensions() and XGetFontPath(). The length field is considered as a signed value, which makes the library access memory before the intended buffer. An attacker who can either configure a malicious X server or modify the data coming from one could use this flaw to make the program crash or have other unspecified effects, caused by the memory corruption.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2019-08-06 19:19:39 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:	1623243, 1623244, 1624412, 1850154, 1875944
Bug Blocks:	1623253

Description Laura Pardo 2018-08-28 20:07:56 UTC

An issue was discovered in libX11 through 1.6.5. Functions ListExt.c:XListExtensions and GetFPath.c:XGetFontPath interpret a variable as signed instead of unsigned, resulting in an out-of-bounds write (of up to 128 bytes), leading to DoS or remote code execution.


References:
http://www.openwall.com/lists/oss-security/2018/08/21/6
https://lists.x.org/archives/xorg-announce/2018-August/002916.html


Upstream Patch:
https://cgit.freedesktop.org/xorg/lib/libX11/commit/?id=dbf72805fd9d7b1846fe9a11b46f3994bfc27fea

Comment 1 Laura Pardo 2018-08-28 20:08:29 UTC

Created libX11 tracking bugs for this issue:

Affects: fedora-all [bug 1623243]

Comment 4 Riccardo Schirone 2018-08-31 13:42:15 UTC

Functions ListExt.c:XListExtensions and GetFPath.c:XGetFontPath interpret the length field, which is a char, as a signed value, resulting in a read and a write before the intended buffer when they traverse the list of extensions/paths provided by the server.

Comment 6 Shiva Prasad Rao 2019-01-29 23:32:20 UTC

Is the fix going to be ported to RHEL 7?

Comment 7 errata-xmlrpc 2019-08-06 12:11:28 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2019:2079 https://access.redhat.com/errata/RHSA-2019:2079

Comment 8 Product Security DevOps Team 2019-08-06 19:19:39 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-2018-14600

Comment 12 Riccardo Schirone 2020-12-03 17:01:34 UTC

Statement:

To exploit the vulnerability an attacker would need to have already compromised the X server used by your applications. Normally, the X client that runs libX11 and the X server runs on the same machine, thus if an attacker can trigger this flaw he has already compromised the X server, which runs as root, and he has already full control on the system. If the X client runs on another system than the X server (e.g. DISPLAY environment variable is used and it points to an X server on another system) then exploiting this vulnerability would only gain the privileges of the client, which should not be run with high privileges.  For the above reasons, this flaw was rated as Moderate Impact.