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Bug 1623238 - (CVE-2018-14598) CVE-2018-14598 libX11: Crash on invalid reply in XListExtensions in ListExt.c
CVE-2018-14598 libX11: Crash on invalid reply in XListExtensions in ListExt.c
Status: NEW
Product: Security Response
Classification: Other
Component: vulnerability (Show other bugs)
unspecified
All Linux
medium Severity medium
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Assigned To: Red Hat Product Security
impact=moderate,public=20180821,repor...
: Security
Depends On: 1623239 1623240 1624389
Blocks: 1623253
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Reported: 2018-08-28 16:02 EDT by Laura Pardo
Modified: 2018-09-19 08:37 EDT (History)
22 users (show)

See Also:
Fixed In Version: libX11 1.6.6
Doc Type: If docs needed, set a value
Doc Text:
It was discovered that libX11 does not properly validate input coming from the server, causing XListExtensions() and XGetFontPath() functions to produce an invalid list of elements that in turn make XFreeExtensionsList() and XFreeFontPath() access invalid memory. An attacker who can either configure a malicious X server or modify the data coming from one, could use this flaw to crash the application using libX11, resulting in a denial of service.
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Description Laura Pardo 2018-08-28 16:02:21 EDT 
An issue was discovered in ListExt.c:XListExtensions and GetFPath.c:XGetFontPath in libX11 through version 1.6.5. A malicious server can send a reply in which the first string overflows, causing a variable to be set to NULL that will be freed later on, leading to DoS (segmentation fault).


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=e83722768fd5c467ef61fa159e8c6278770b45c2
Comment 1 Laura Pardo 2018-08-28 16:02:59 EDT 
Created libX11 tracking bugs for this issue:

Affects: fedora-all [bug 1623239]
Comment 3 Riccardo Schirone 2018-08-31 07:47:47 EDT 
When a reply from a malicious server has the first element with an invalid length, the ListExt.c:XListExtensions and GetFPath.c:XGetFontPath functions may wrongly initialize the returned list. Thus a following call to XFreeExtensionsList/XFreeFontPath will try to access an invalid list, causing a segmentation fault in the client program.
Comment 6 Riccardo Schirone 2018-09-03 05:51:45 EDT 
Statement:

This issue did not affect the versions of libX11 as shipped with Red Hat Enterprise Linux 5 as they did not include the vulnerable code.
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