Security News > 2021 > December > Microsoft December 2021 Patch Tuesday fixes 6 zero-days, 67 flaws

Today is Microsoft's December 2021 Patch Tuesday, and with it comes fixes for six zero-day vulnerabilities and a total of 67 flaws.
Microsoft has fixed 55 vulnerabilities with today's update, with seven classified as Critical and 60 as Important.
December's Patch Tuesday includes fixes for six zero-day vulnerabilities, with one actively exploited Windows AppX Installer vulnerability.
Microsoft classifies a vulnerability as a zero-day if it is publicly disclosed or actively exploited with no official fix available.
Microsoft also fixed five publicly disclosed zero-day vulnerabilities as part of the December 2021 Patch Tuesday that are not known to be exploited in attacks.
Below is the complete list of resolved vulnerabilities and released advisories in the December 2021 Patch Tuesday updates.
News URL
Related news
- Microsoft February 2025 Patch Tuesday fixes 4 zero-days, 55 flaws (source)
- Patch Tuesday: Microsoft Patches Two Actively Exploited Zero-Day Flaws (source)
- Microsoft March 2025 Patch Tuesday fixes 7 zero-days, 57 flaws (source)
- Patch Tuesday: Microsoft Fixes 57 Security Flaws – Including Active Zero-Days (source)
- February's Patch Tuesday sees Microsoft offer just 63 fixes (source)
- Microsoft’s Patch Tuesday Fixes 63 Flaws, Including Two Under Active Exploitation (source)
- Choose your own Patch Tuesday adventure: Start with six zero day fixes, or six critical flaws (source)
- April 2025 Patch Tuesday forecast: More AI security introduced by Microsoft (source)
- February 2025 Patch Tuesday forecast: New directions for AI development (source)
- Microsoft fixes two actively exploited zero-days (CVE-2025-21418, CVE-2025-21391) (source)