CVE-2016-3309

CVE-2016-3309 is a privilege escalation vulnerability in the Microsoft Windows kernel caused by improper handling of objects in memory. Triggering it typically requires getting crafted code to run on the system (the usual pattern for kernel EoP flaws), after which the kernel mishandles the objects and the attacker can execute arbitrary code in kernel mode. Successful exploitation grants full system-level privileges, letting an attacker disable security tooling, steal credentials, and deploy payloads such as ransomware. CISA lists the affected product broadly as Microsoft Windows, with older and legacy Windows builds being the most likely remaining targets for this 2016-era flaw. Exploitation is confirmed in the wild: the flaw was added to the CISA KEV catalog on 2022-03-15 with known ransomware use, and EPSS assigns a 20.6% probability of exploitation in the next 30 days (97th percentile).

What to do: Apply Microsoft's kernel-mode security updates per vendor instructions on all Windows systems, prioritizing legacy/out-of-support builds where this flaw is most likely to remain unpatched. Since the bug is KEV-listed with known ransomware use, verify patch deployment fleet-wide and inventory any Windows hosts that can no longer receive updates, isolating them or applying compensating controls. There is no public PoC, but treat unpatched Windows endpoints with local user or execution access as high priority for remediation.