CVE-2019-15316: Valvesoftware Steam Client

High severity, CVSS 7.0. EPSS: 0.4% chance of exploitation in the next 30 days.

Valve Steam Client for Windows through 2019-08-20 has weak folder permissions, leading to privilege escalation (to NT AUTHORITY\SYSTEM) via crafted use of CreateMountPoint.exe and SetOpLock.exe to leverage a TOCTOU race condition.

Affected products

• Valvesoftware Steam Client: up to and including 2019-08-20

Published 2019-08-21. Last modified 2026-06-17.