CVE-2020-15530 in Steam Client
Summary
by MITRE
An issue was discovered in Valve Steam Client 2.10.91.91. The installer allows local users to gain NT AUTHORITY\SYSTEM privileges because some parts of %PROGRAMFILES(X86)%\Steam and/or %COMMONPROGRAMFILES(X86)%\Steam have weak permissions during a critical time window. An attacker can make this time window arbitrarily long by using opportunistic locks.
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Analysis
by VulDB Data Team • 07/06/2020
The vulnerability identified as CVE-2020-15530 represents a critical privilege escalation flaw within the Valve Steam Client installation process. This issue affects version 2.10.91.91 and stems from inadequate permission controls during the installation lifecycle. The vulnerability exploits the Windows file system by targeting directories within the Program Files and Common Program Files directories where Steam components are installed. During the installation process, certain directories maintain weak security permissions that create a window of opportunity for local attackers to manipulate the system. The flaw specifically manifests when Steam installer executes operations in %PROGRAMFILES(X86)%\Steam and/or %COMMONPROGRAMFILES(X86)%\Steam, where temporary or critical installation files may be accessible with insufficient access controls.
The technical exploitation mechanism leverages opportunistic locking techniques combined with race conditions inherent in the installation process. Attackers can extend the vulnerable time window indefinitely by implementing opportunistic locks, which effectively prolongs the period during which weak permissions remain active. This approach allows adversaries to perform malicious file replacement or modification operations against Steam installation directories before the system properly secures these locations. The vulnerability operates at the operating system level, specifically targeting Windows file permission models and the timing of installation processes. The weakness lies in the lack of proper atomic operations during installation, where critical system components are not adequately protected during the transition from installation to operational state.
The operational impact of this vulnerability is severe as it allows local users to escalate their privileges to the highest system level authority, specifically NT AUTHORITY\SYSTEM. This privilege escalation enables attackers to perform any action on the compromised system, including installing malicious software, modifying system files, accessing sensitive data, and potentially establishing persistent backdoors. The attack vector requires only local system access, making it particularly dangerous in environments where user accounts may be compromised through other means. The vulnerability affects all users of the affected Steam client version regardless of their initial privilege level, creating a widespread security concern for organizations and individual users alike.
Mitigation strategies for CVE-2020-15530 should focus on immediate remediation through official Steam client updates from Valve, which would address the underlying permission handling during installation. System administrators should implement restrictive file permissions on Steam installation directories and monitor for unauthorized modifications to these locations. The principle of least privilege should be enforced by ensuring that installation processes run with minimal required permissions rather than elevated privileges throughout the entire process. Additionally, organizations should consider implementing endpoint protection solutions that can detect and prevent suspicious file manipulation activities in Program Files directories. This vulnerability aligns with CWE-276, which addresses improper file permissions, and maps to ATT&CK technique T1068, privilege escalation through local exploitation. Regular security audits of installed software should include verification of file permissions and proper installation process integrity to prevent similar vulnerabilities from being exploited in other applications.