CVE-2021-43217CriticalCVSS 8.1

Windows Encrypting File System (EFS) Remote Code Execution Vulnerability

Published
December 14, 2021
Last Modified
—

🔗 CVE IDs covered (1)

CVE-2021-43217 →

📋 Description

What is the attack vector for this vulnerability? An attacker could cause a buffer overflow write leading to unauthenticated non-sandboxed code execution. Does EFS need to be in use for this to be exploited? No. EFS interfaces trigger a start to the EFS service if it isn’t already running. How does Microsoft plan to address this vulnerability? Microsoft is addressing the vulnerability in a phased two-part rollout. These updates address the vulnerability by modifying how EFS makes connections from client to server. For guidelines on how to manage the changes required for this vulnerability and more information on the phased rollout, see KB5009763: EFS security hardening changes in CVE-2021-43217. When the second phase of Windows updates become available in Q1 2022, customers will be notified via a revision to this security vulnerability. If you wish to be notified when these updates are released, we recommend that you register for the security notifications mailer to be alerted of content changes to this advisory. See Microsoft Technical Security Notifications. How do the two deployment phases address the vulnerability? The initial deployment phase starts with the Windows updates released on December 14, 2021. The updates will enable packet-level privacy for EFS when the client initiates a connection, and the server will only allow connections with packet-level privacy. The second phase, planned for a Q1 2022 release, marks the transition into the enforcement phase. Support for the AllowAllCliAuth registry key will be removed and servers will require packet-level privacy regardless of the registry key setting. Is there a recommended order in which I should install these updates on client and server machines? Yes. We recommend that you install the security updates to address this vulnerability on client machines first and then on servers.

🎯 Affected products46

  • Windows 10 Version 1607 for 32-bit Systems
  • Windows 10 Version 1607 for x64-based Systems
  • Windows 10 Version 1809 for 32-bit Systems
  • Windows 10 Version 1809 for ARM64-based Systems
  • Windows 10 Version 1809 for x64-based Systems
  • Windows 10 Version 1909 for 32-bit Systems
  • Windows 10 Version 1909 for ARM64-based Systems
  • Windows 10 Version 1909 for x64-based Systems
  • Windows 10 Version 2004 for 32-bit Systems
  • Windows 10 Version 2004 for ARM64-based Systems
  • Windows 10 Version 2004 for x64-based Systems
  • Windows 10 Version 20H2 for 32-bit Systems
  • Windows 10 Version 20H2 for ARM64-based Systems
  • Windows 10 Version 21H1 for 32-bit Systems
  • Windows 10 Version 21H1 for ARM64-based Systems
  • Windows 10 Version 21H1 for x64-based Systems
  • Windows 10 Version 21H2 for 32-bit Systems
  • Windows 10 Version 21H2 for ARM64-based Systems
  • Windows 10 Version 21H2 for x64-based Systems
  • Windows 10 for 32-bit Systems
  • Windows 10 for x64-based Systems
  • Windows 11 version 21H2 for ARM64-based Systems
  • Windows 11 version 21H2 for x64-based Systems
  • Windows 7 for 32-bit Systems Service Pack 1
  • Windows 7 for x64-based Systems Service Pack 1
  • Windows 8.1 for 32-bit systems
  • Windows 8.1 for x64-based systems
  • Windows RT 8.1
  • Windows Server 2008 R2 for x64-based Systems Service Pack 1
  • Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation)
  • +16 more not shown

✅ Remediation

KB5008218 (Security Update) — fixed build 10.0.17763.2366 KB5008206 (Security Update) — fixed build 10.0.18363.1977 KB5008212 (Security Update) — fixed build 10.0.19043.1415 KB5008223 (Security Update) — fixed build 10.0.20348.405 KB5008212 (Security Update) — fixed build 10.0.19041.1415 KB5008212 (Security Update) — fixed build 10.0.19042.1415 KB5008215 (Security Update) — fixed build 10.0.22000.376 KB5008212 (Security Update) — fixed build 10.0.19044.1415 KB5008230 (Security Update) — fixed build 10.0.10240.19145 KB5008207 (Security Update) — fixed build 10.0.14393.4825 KB5008244 (Monthly Rollup) — fixed build 6.1.7601.25796 KB5008282 (Security Only) — fixed build 6.1.7601.25796 KB5008263 (Monthly Rollup) — fixed build 6.3.9600.20207 KB5008285 (Security Only) — fixed build 6.3.9600.20207 KB5008274 (Monthly Rollup) — fixed build 6.0.6003.21309 KB5008271 (Security Only) — fixed build 6.0.6003.21309 KB5008277 (Monthly Rollup) — fixed build 6.2.9200.23545 KB5008255 (Security Only) — fixed build 6.2.9200.23540

🔗 References (28)