CVE-2016-5237 in Steam
Summary
by MITRE
Valve Steam 3.42.16.13 uses weak permissions for the files in the Steam program directory, which allows local users to modify the files and possibly gain privileges as demonstrated by a Trojan horse Steam.exe file.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2016-5237 affects Valve Steam client version 3.42.16.13 and represents a critical privilege escalation flaw stemming from inadequate file system permissions within the Steam program directory. This weakness allows local attackers to manipulate critical installation files, potentially enabling them to execute malicious code with elevated privileges. The vulnerability specifically manifests through the use of weak permissions that permit unauthorized modification of essential Steam components, creating a persistent attack vector that can be exploited by adversaries with local system access. The flaw demonstrates a fundamental failure in the software's security model, where the installation directory lacks proper access controls that should prevent unauthorized modifications to core application files. This issue directly violates security best practices for software installation and privilege management, as the Steam client fails to implement appropriate file permission controls that would normally protect against such modifications.
The technical implementation of this vulnerability involves the Steam client's installation directory containing files with overly permissive access controls that allow any local user to modify critical executable components. When an attacker places a malicious Trojan horse Steam.exe file in the program directory, the system may execute this modified version instead of the legitimate one, effectively enabling privilege escalation. The weak permissions create a situation where standard user accounts can manipulate files that should remain protected from modification, fundamentally undermining the security boundary between user and system privileges. This type of vulnerability aligns with CWE-276, which describes improper file permissions, and represents a classic example of inadequate access control implementation in software installations. The flaw operates at the operating system level where file permissions are not properly enforced, allowing local users to gain unauthorized access to system resources through manipulation of the application's own installation files.
The operational impact of CVE-2016-5237 extends beyond simple privilege escalation to encompass potential system compromise and data theft capabilities. Attackers leveraging this vulnerability can establish persistent backdoors through the modified Steam executable, potentially maintaining access to compromised systems for extended periods. The vulnerability also enables code injection attacks where malicious payloads can be executed with the privileges of the Steam client process, which typically runs with elevated permissions. This creates a significant risk for users who may unknowingly download and execute compromised versions of the Steam client or install malicious software through legitimate-looking updates. The attack vector is particularly concerning because it leverages the trust relationship between the user and the legitimate software, making detection more difficult. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and persistence mechanisms, specifically targeting the execution and privilege escalation phases of an attack lifecycle. The vulnerability affects not only individual user systems but also enterprise environments where Steam clients may be deployed across multiple machines, potentially providing attackers with access to entire networks through a single compromised client installation.
Mitigation strategies for CVE-2016-5237 require immediate implementation of proper file permissions and access control measures. System administrators should ensure that Steam installation directories are configured with appropriate permissions that prevent unauthorized modification of executable files, typically by setting restrictive permissions that only allow administrators to modify core components. The recommended approach involves implementing proper file ownership controls and access control lists that enforce least privilege principles for the Steam program directory. Users should be encouraged to regularly update their Steam client to versions that address this vulnerability, as Valve released patches to correct the weak permission settings. Additionally, organizations should implement application whitelisting policies that restrict execution of unauthorized software, particularly in environments where multiple users have access to shared systems. Network monitoring should be enhanced to detect suspicious execution patterns that may indicate exploitation attempts, including unusual process creation or file modification activities in the Steam installation directory. The vulnerability also highlights the importance of regular security audits of installed applications to identify and remediate similar permission-related flaws that may exist in other software installations. Proper system hardening practices should include verification of file integrity checks and implementation of automatic updates that maintain secure permission settings across all system components.