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CVE-2021-1647Microsoft Defender Remote Code Execution VulnerabilityUpdated monthlyMicrosoft Patch Tuesday
Microsoft Patch Tuesday
January 2021
Microsoft's January 2021 Patch Tuesday fixes 82 vulnerabilities across Windows, Microsoft Office and Developer Tools - 9 rated Critical, 1 publicly disclosed before the patch shipped, one already exploited in the wild. Patch CVE-2021-1647 first.
Released January 12, 2021, 10:00 PT1 actively exploited1 publicly disclosed67 KB articles to deploy
January 2021 Patch Tuesday at a glance
82
Microsoft CVEs
excl. Edge & Azure Linux
9
Critical
11% of the release
1
Actively exploited
CVE-2021-1647
1
Publicly disclosed
known before the patch
8.8
Highest CVSS
CVE-2021-1707
67
KB articles
what you actually deploy
Why this number differs from other roundups. Microsoft's January 2021 release document lists 196 entries. 89 are Azure Linux (Mariner) OS package updates and 25 are republished Chromium fixes for Edge - neither is a Microsoft product vulnerability. The 82 above is the real Patch Tuesday set. See the breakdown →
Priority order
Patch these first
Ranked by exploitation reality, not score alone. This month's exploited flaw is rated Critical - a severity-sorted list would bury it.
Patch this week
Publicly disclosed
Details are already public. Working exploits typically follow within days.
CVE-2021-1648Microsoft splwow64 Elevation of Privilege VulnerabilityPatch this cycle
Critical remote code execution
No known exploitation yet, but network-reachable and high impact.
CVE-2021-1658Remote Procedure Call Runtime Remote Code Execution VulnerabilityCVE-2021-1660Remote Procedure Call Runtime Remote Code Execution VulnerabilityCVE-2021-1666Remote Procedure Call Runtime Remote Code Execution VulnerabilitySee all 9 Critical →The numbers
What’s in this release
Where the 196 entries actually come from
Most roundups quote a single number. These are three unrelated release streams.
82
89
25
82 Microsoft products89 Azure Linux (Mariner)25 Edge (Chromium)
Severity
Microsoft channel only · 82 CVEs
| Critical | 9 |
|---|---|
| Important | 73 |
| Moderate | 0 |
| Low | 0 |
Impact type
What an attacker gains if it works
| Elevation of Privilege | 34 |
|---|---|
| Remote Code Execution | 23 |
| Information Disclosure | 11 |
| Security Feature Bypass | 5 |
| Spoofing | 4 |
| Denial of Service | 4 |
| Tampering | 1 |
Most-affected components
Where this month’s fixes concentrate - filter by any of them in the table below
Windows Remote Procedure Call Runtime9Microsoft Windows8Windows CSC Service7Microsoft Office SharePoint6Microsoft Office5Microsoft Graphics Component4Windows WalletService4Microsoft Bluetooth Driver3Windows Hyper-V3Windows Projected File System Filter Driver3Microsoft Windows Codecs Library2Windows AppX Deployment Extensions2
Every patch
Browse all 196 entries
Sorted by risk by default: exploited first, then publicly disclosed, then severity, then CVSS. Search by CVE, title, component or KB number.
| Title | Status | KB | |||||
|---|---|---|---|---|---|---|---|
| Critical | CVE-2021-1647 | Microsoft Defender Remote Code Execution Vulnerability | RCE | 7.8 | Exploited | Microsoft Malware Protection Engine | — |
| Important | CVE-2021-1648 | Microsoft splwow64 Elevation of Privilege Vulnerability | EoP | 7.8 | Disclosed | Windows splwow64 | 4598229 +9 |
| Important | CVE-2021-1707 | Microsoft SharePoint Server Remote Code Execution Vulnerability | RCE | 8.8 | More likely | Microsoft Office SharePoint | 4493162 +3 |
| Important | CVE-2021-1709 | Windows Win32k Elevation of Privilege Vulnerability | EoP | 7.0 | More likely | Microsoft Graphics Component | 4598229 +13 |
| Critical | CVE-2021-1658 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Critical | CVE-2021-1660 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Critical | CVE-2021-1666 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Critical | CVE-2021-1667 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Critical | CVE-2021-1673 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Critical | CVE-2021-1643 | HEVC Video Extensions Remote Code Execution Vulnerability | RCE | 7.8 | — | Microsoft Windows Codecs Library | — |
| Critical | CVE-2021-1665 | GDI+ Remote Code Execution Vulnerability | RCE | 7.8 | — | Microsoft Graphics Component | 4598229 +13 |
| Critical | CVE-2021-1668 | Microsoft DTV-DVD Video Decoder Remote Code Execution Vulnerability | RCE | 7.8 | — | Microsoft DTV-DVD Video Decoder | 4598229 +11 |
| Important | CVE-2021-1636 | Microsoft SQL Elevation of Privilege Vulnerability | EoP | 8.8 | — | SQL Server | 4583456 +8 |
| Important | CVE-2021-1664 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Important | CVE-2021-1669 | Windows Remote Desktop Security Feature Bypass Vulnerability | Bypass | 8.8 | — | Windows Remote Desktop | 4598229 +5 |
| Important | CVE-2021-1671 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Important | CVE-2021-1674 | Windows Remote Desktop Protocol Core Security Feature Bypass Vulnerability | Bypass | 8.8 | — | Windows Remote Desktop | 4598229 +11 |
| Important | CVE-2021-1678 | Windows Print Spooler Spoofing Vulnerability | Spoofing | 8.8 | — | Windows NTLM | 4598229 +14 |
| Important | CVE-2021-1700 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Important | CVE-2021-1701 | Remote Procedure Call Runtime Remote Code Execution Vulnerability | RCE | 8.8 | — | Windows Remote Procedure Call Runtime | 4598229 +13 |
| Important | CVE-2021-1712 | Microsoft SharePoint Elevation of Privilege Vulnerability | EoP | 8.0 | — | Microsoft Office SharePoint | 4493162 +2 |
| Important | CVE-2021-1718 | Microsoft SharePoint Server Tampering Vulnerability | Tampering | 8.0 | — | Microsoft Office SharePoint | 4493187 |
| Important | CVE-2021-1719 | Microsoft SharePoint Elevation of Privilege Vulnerability | EoP | 8.0 | — | Microsoft Office SharePoint | 4493162 +1 |
| Important | CVE-2021-1642 | Windows AppX Deployment Extensions Elevation of Privilege Vulnerability | EoP | 7.8 | — | Windows AppX Deployment Extensions | 4598229 +4 |
| Important | CVE-2021-1644 | HEVC Video Extensions Remote Code Execution Vulnerability | RCE | 7.8 | — | Microsoft Windows Codecs Library | — |
Your move
What your IT team should do
The same five steps every month, in the order that reduces risk fastest.
Triage by exploitability, not CVSS
CVE-2021-1647 is rated Critical and scores 7.8 - a CVSS-sorted list would bury the one flaw attackers are already using. Sort by exploited, then publicly disclosed, then severity.
Patch Management vs Vulnerability Management: What's the Difference? →Stage the rollout in rings
This release means 67 distinct update packages to deploy. Pilot on ring 0 within 24 hours and widen to production by day seven - never push the whole set everywhere at once.
What is Ring-Based Patch Deployment? A Guide to Progressive Rollouts →The Patch Management Lifecycle: 6 Stages from Discovery to Verification →Test the known-issue candidates
Check the Windows release health dashboard before promoting past ring 1, and have the rollback path written down before you need it. Kernel, networking and authentication fixes are the ones that historically break things.
12 Patch Management Best Practices for 2026 →Don't stop at the operating system
25 Chromium fixes for Edge shipped alongside this release on their own updater, and Adobe, SAP and Oracle release in the same week. OS-only patching leaves most of your real attack surface untouched.
What is Third-Party Patch Management and Why OS Patching Isn't Enough →Verify installed state, then evidence it
Confirm the patch is actually present on each endpoint rather than trusting that "deployment succeeded". Keep the resulting report - it is the artefact auditors ask for, and reconstructing it later is far more work than capturing it now.
Patch Management: The Complete Guide →Trinetri does steps two through five automatically - detecting the 67 KB articles across every endpoint, staging them in rings, verifying installed state and producing the compliance evidence. See patch management →
Archive
Previous Patch Tuesdays
Every month Microsoft has published back to January 2016, each with the same breakdown and the full CVE list.
October 2026October 13, 2026September 2026September 8, 2026August 2026August 11, 2026July 2026July 14, 2026June 2026June 9, 2026May 2026May 12, 2026April 2026April 14, 2026March 2026March 10, 2026February 2026February 10, 2026January 2026January 13, 2026December 2025December 9, 2025November 2025November 11, 2025October 2025October 14, 2025September 2025September 9, 2025August 2025August 12, 2025July 2025July 8, 2025June 2025June 10, 2025May 2025May 13, 2025April 2025April 8, 2025March 2025March 11, 2025February 2025February 11, 2025January 2025January 14, 2025December 2024December 10, 2024November 2024November 12, 2024
Older months104 releases, October 2024 – January 2016
2024
2023
2022
2021
2020
2019
2018
2017
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Patch Tuesday FAQ
Patch Tuesday falls on the second Tuesday of every month, with updates going live at 10:00 a.m. Pacific Time. Microsoft introduced the practice in October 2003, following the Blaster worm, to cut distribution costs and give administrators a predictable cadence instead of patches arriving at random. The 10:00 a.m. timing is deliberate: it leaves a full working week to remediate before the weekend. Internally Microsoft calls it the "B" release; optional "C" and "D" preview releases follow later in the month. The next Patch Tuesday is November 10, 2026.
Microsoft fixed 82 vulnerabilities in January 2021, across Windows, Microsoft Office, Developer Tools and Apps. 9 are rated Critical, 1 were publicly disclosed before the patch shipped, and 1 was already being exploited. Note that Microsoft's release document lists 196 entries in total, but 89 of those are Azure Linux package updates and 25 are republished Chromium fixes for Edge, which is why other sources sometimes quote a much larger number.
Exploit Wednesday is the day after Patch Tuesday. Attackers compare the newly released patches against the previous version to locate the flaw each one fixes, then build working exploits from that difference - often within 24 to 48 hours. It is the reason the deployment window matters as much as the patch itself: every hour a Critical remote code execution fix sits undeployed is an hour of measurable exposure.
A workable target for most organisations: actively exploited vulnerabilities within 24 hours, publicly disclosed ones within 72 hours, remaining Critical fixes within seven days, and everything else within the month. CISA's Known Exploited Vulnerabilities catalogue sets binding deadlines for US federal agencies and is a reasonable benchmark for everyone else. Stage the rollout in rings rather than deploying everywhere at once, so a regression is caught on a pilot group instead of in production.
An out-of-band update is a patch released outside the monthly cycle because the risk will not wait for the next Patch Tuesday. Microsoft issues them for actively exploited flaws with no mitigation - most famously during the WannaCry outbreak in 2017, when it took the unusual step of patching versions of Windows that were already out of support.
Yes. Adobe aligned its releases with Patch Tuesday in November 2012, and both SAP's Security Patch Day and Oracle's quarterly Critical Patch Updates are coordinated to the same week. Part of the reason is defensive: staggered releases let attackers reverse-engineer one vendor's patch to find the same underlying flaw in another's still-unpatched product. For IT teams it means the second Tuesday is rarely just a Microsoft problem.
Edge is built on Chromium, so most of its security fixes originate with the Chromium project and are republished by Microsoft under their own CVE identifiers. They ship on Chromium's cadence rather than the Patch Tuesday cycle, and they are delivered by Edge's own updater rather than Windows Update. Counting the 25 Edge entries alongside Microsoft product fixes would inflate the headline number and imply work for your Windows Update rings that does not exist.