Steam vulnerability on Windows lets any normal user silently escalate to SYSTEM
Source Reddit Cybersecurity
Rated by Threat Radar
Data as of 15 Sep 2026, 00:46 UTC
What to do
AI-suggested
Until a fix is available, restrict unprivileged user access to affected systems or consider disabling the Steam Client Service if feasible.
Discussion
A local privilege escalation vulnerability in the Steam Client Service on Windows 10 and 11 allows any standard user to silently escalate privileges to SYSTEM without requiring admin rights, UAC prompts, or launching a game. The issue stems from a signature verification gap in Steam's installation process, enabling execution of code as SYSTEM without signature forgery. This was tested on Steam version 10.96.30.42. Valve was notified months prior to public disclosure.
r/cybersecurity (opens in a new tab)u/xBeT3rDx0 points0 comments
A newly disclosed local privilege escalation (LPE) in the Steam Client Service affects Windows 10 and 11. Any standard, unprivileged user can get a SYSTEM-level shell — no admin rights, no UAC prompt, no game launch required.
The root cause is a signature coverage gap in Steam's installation verification. The exploit passes a caller-controlled path that Valve's signed VDF never actually covers, letting you run code as SYSTEM without touching or forging the signature at all.
Tested on Steam version 10.96.30.42.
Tagging this as educational/defensive research, but worth mentioning that Valve were notified about this months ago.