Privilege Escalation in Microsoft Desktop Window Manager (DWM) Core Library (CVE‑2021‑33739)
What It Is
CVE‑2021‑33739 is a privilege‑escalation flaw in the Microsoft Desktop Window Manager (DWM) Core Library. The vulnerability allows a low‑privileged user or process to gain higher‑level system rights on Windows devices. Microsoft addressed the issue with a security update released in August 2021.
Exploitability
- No public proof‑of‑concept has been released, and there is no evidence of active exploitation in the wild.
- The vulnerability is classified as High severity (CVSS v3.1 base score 7.8). Exploitation requires local access to the target system, making it a concern for environments where untrusted users or applications run on shared workstations.
Affected Products
- Microsoft Windows (all supported client and server versions that include the DWM Core Library prior to the August 2021 patch).
Why It Matters for Compliance & Audit Readiness
- Access Controls: Privilege‑escalation bypasses the principle of least privilege, undermining controls mapped to NIST 800‑53 AC‑6 and ISO 27001 A.9.2.1.
- Continuous Monitoring: Detecting anomalous privilege changes is a key control in a robust monitoring program; failure to remediate leaves gaps in audit evidence.
- Defensible Evidence: Demonstrating timely patch application and verification of privileged‑account activity provides a clear, auditable trail for regulators and internal reviewers.
Recommended Actions
- Patch Management: Verify that the August 2021 security update (or later cumulative updates) is installed on all Windows endpoints. Capture patch‑status reports as evidence of due‑diligence.
- Control Mapping: Align the remediation to your access‑control framework (e.g., map to AC‑6, AC‑2). Document the control update in your risk register.
- Validate Post‑Remediation Posture: Run a privileged‑account audit to confirm no unexpected elevation events occurred after patching. Log the results for audit readiness.
- Continuous Monitoring: Enable and tune Windows Event Log collection for “Privilege Use” events (4624, 4670) to detect any future attempts.
Source: CISA KEV – CVE‑2021‑33739