CISA Orders Federal Agencies to Patch Actively Exploited Windows Vulnerability

CVE-2021-1732 is a local elevation-of-privilege vulnerability (CWE-787, out-of-bounds write) in Microsoft's Win32k kernel driver, publicly characterized as an "offset confusion" in the Win32k ConsoleControl routine. It is triggered locally: a process with only low privileges can invoke the vulnerable Win32k functionality without any user interaction, causing a user-supplied offset/pointer to be mishandled in kernel mode and memory to be written out of bounds. An attacker who successfully exploits the flaw can execute code in the kernel and elevate to SYSTEM, gaining full control of the host — which makes it a valuable second-stage link in malware and ransomware chains. Any system running the affected Windows 10 releases (1803, 1809, 1909, 2004, 20H2) or Windows Server 2019/1909/2004/20H2 is exposed, though exploitation requires the attacker to already run code locally on the target. The flaw was fixed in Microsoft's February 2021 Patch Tuesday updates, was added to CISA's KEV catalog on 2021-11-03 with known ransomware use, and carries a very high EPSS score (78.4%, 100th percentile), indicating sustained exploitation pressure.

Do: Apply Microsoft's February 2021 (or later) Windows cumulative security updates to all affected Windows 10 and Windows Server systems, per vendor instructions — CISA's KEV listing requires federal agencies to patch. Prioritize hosts exposed to untrusted local users or already compromised by malware (e.g., ransomware or Raspberry Robin activity, which has used chained Windows LPEs), and hunt on unpatched hosts for signs of post-exploitation privilege escalation to SYSTEM.

CVE-2022-21882 is a Win32k elevation-of-privilege vulnerability caused by an out-of-bounds write (CWE-787) in the Windows kernel's Win32k component, affecting Windows 10 versions 1809 through 21H2, Windows 11 21H2, and Windows Server 2019, 2022, and version 20H2. A local attacker who can already execute code with a low-privileged account can trigger the flaw via Win32k system calls with no user interaction, corrupting kernel memory and escalating to SYSTEM-level privileges. Successful exploitation gives the attacker full control of the compromised host (high confidentiality, integrity, and availability impact), and it is commonly chained after an initial foothold to deploy ransomware or other payloads. Anyone running the affected Windows 10, Windows 11, or Windows Server builds is exposed, because the vulnerable Win32k code ships by default with those operating systems. The flaw is actively exploited in the wild: it is in CISA's Known Exploited Vulnerabilities catalog (added 2022-02-04) with known ransomware use, and public proof-of-concept code was released by researchers after disclosure.

Do: Apply Microsoft's cumulative security updates for Windows 10 (1809–21H2), Windows 11 21H2, and Windows Server 2019/2022/20H2 immediately — the fix shipped in Microsoft's January 2022 Patch Tuesday and is included in all later cumulative updates; per CISA's required action, apply updates per vendor instructions. Prioritize multi-user hosts (RDS/VDI, terminal and jump servers) where local privilege escalation is most damaging, and hunt for post-compromise indicators such as unexpected SYSTEM-level processes, since ransomware operators are known to use this bug after gaining an initial foothold. If patching is delayed, limit local code execution on affected systems and watch EDR telemetry for kernel-level privilege-escalation behavior.