What attackers do. Attackers exploit a software bug, often in the operating system kernel, a driver or a privileged service, to raise their access from a normal user to administrator or system level. This serves the Privilege Escalation tactic and sometimes Defence Evasion.
How to defend. Patch operating systems, drivers and privileged software promptly, and use vulnerable driver blocklists to stop attackers loading known-flawed signed drivers. Limit local admin rights so that exploitation is needed at all, and enable exploit protection features available in the platform. Endpoint detection tools that monitor process integrity levels and driver loads give the best visibility.
Signs to look for. Watch for a low-privilege process suddenly spawning a child running as system, unexpected driver installations, and crashes of privileged services just before suspicious activity. Gaps often come from unpatched legacy hosts and from not alerting on driver loads at all.