Bug 1623022 – CVE-2018-15857 libxkbcommon: Invalid free in ExprAppendMultiKeysymList resulting in a crash

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Bug 1623022 - (CVE-2018-15857) CVE-2018-15857 libxkbcommon: Invalid free in ExprAppendMultiKeysymList resulting in a crash

Summary:	CVE-2018-15857 libxkbcommon: Invalid free in ExprAppendMultiKeysymList result...

Status:	NEW

Aliases:	CVE-2018-15857

Product:	Security Response
Classification:	Other
Component:	vulnerability (Show other bugs)
Sub Component:
Version:	unspecified
Hardware:	All Linux

Priority	medium Severity medium
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Assigned To:	Red Hat Product Security
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Whiteboard:	impact=moderate,public=20180730,repor...
Keywords:	Security

Depends On:	1623038 1643153
Blocks:	1623044
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Reported:	2018-08-28 07:54 EDT by Andrej Nemec
Modified:	2018-10-25 11:30 EDT (History)
CC List:	3 users (show)

See Also:
Fixed In Version:	libxkbcommon 0.8.1
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Description Andrej Nemec 2018-08-28 07:54:06 EDT

An invalid free in ExprAppendMultiKeysymList in xkbcomp/ast-build.c in xkbcommon before 0.8.1 could be used by local attackers to crash xkbcommon keymap parsers or possibly have unspecified other impact by supplying a crafted keymap file.

Upstream patch:

https://github.com/xkbcommon/libxkbcommon/commit/c1e5ac16e77a21f87bdf3bc4dea61b037a17dddb

References:

https://lists.freedesktop.org/archives/wayland-devel/2018-August/039232.html

Comment 3 Riccardo Schirone 2018-10-25 11:30:25 EDT

ExprAppendMultiKeysymList() in xkbcomp/ast-build.c appends a list of KeySymbols to an existing one and frees it after doing so. However, the address of the pointer to the KeySyms expression is passed to the FreeStmt() function, instead of the pointer itself, causing a free on an invalid area. An attacker, by creating a special xkb keymap file, may be able to use this flaw to crash the program or execute code.

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