Valve Steam Client Application v1559/1559 Local Privilege Escalation

Vendor: Valve Corporation

Product web page: http://www.steampowered.com

Affected version: Built: Jun 1, 2011 at 15:31:24
                  Steam API: v010
                  Steam package versions 1559 / 1559
                  File version: 1.0.968.628

Summary: Steam is a digital distribution, digital rights management,
multiplayer and communications platform developed by Valve Corporation.
It is used to distribute games and related media online, from small
independent developers to larger software houses. Steam also has
community features, automated game updates, and in-game voice and
chat functionality.

Desc: Steam is vulnerable to an elevation of privileges vulnerability
which can be used by a simple user that can change the executable file
with a binary of choice. The vulnerability exist due to the improper
permissions, with the "F" flag (Full Control) for the "Users" group,
for the binary file Steam.exe, GameOverlayUI.exe and steamerrorreporter.exe.
The binary (Steam.exe) is set by default to Startup with "-silent" parameter.

Tested on: Microsoft Windows XP Professional SP3 (EN)

Vendor status:

24.06.2011 - Vulnerability discovered.
25.06.2011 - Initial contact with the vendor.
25.06.2011 - Auto-reply from the vendor stating that the message is received.
28.06.2011 - No reply from the vendor.
29.06.2011 - Public security advisory released.

Vulnerability discovered by Gjoko 'LiquidWorm' Krstic
                            liquidworm gmail com

Advisory ID: ZSL-2011-5022
Advisory URL: http://www.zeroscience.mk/en/vulnerabilities/ZSL-2011-5022.php

24.06.2011

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C:\Program Files\Steam>cacls Steam.exe
C:\Program Files\Steam\Steam.exe BUILTIN\Users:F <---
                                 NT AUTHORITY\SYSTEM:F
                                 BUILTIN\Power Users:C
                                 BUILTIN\Administrators:F
                                 LABPC\User101:F