Microsoft's July 2021 Patch Tuesday fixes 120 vulnerabilities across Windows, Microsoft Office and Server Software - 13 rated Critical, 9 publicly disclosed before the patch shipped, 4 already exploited in the wild. Patch CVE-2021-34527 first.
Why this number differs from other roundups. Microsoft's July 2021 release document lists 189 entries. 35 are Azure Linux (Mariner) OS package updates and 34 are republished Chromium fixes for Edge - neither is a Microsoft product vulnerability. The 120 above is the real Patch Tuesday set. See the breakdown →
Ranked by exploitation reality, not score alone. This month's exploited flaw is rated Critical - a severity-sorted list would bury it.
Patch today
Confirmed attacks are already happening. Emergency change window.
CVE-2021-34527Windows Print Spooler Remote Code Execution VulnerabilityCVE-2021-34448Scripting Engine Memory Corruption VulnerabilityCVE-2021-31979Windows Kernel Elevation of Privilege VulnerabilityCVE-2021-33771Windows Kernel Elevation of Privilege VulnerabilityPatch this week
Details are already public. Working exploits typically follow within days.
CVE-2021-34473Microsoft Exchange Server Remote Code Execution VulnerabilityCVE-2021-34481Windows Print Spooler Remote Code Execution VulnerabilityCVE-2021-36934Windows Elevation of Privilege VulnerabilityCVE-2021-34523Microsoft Exchange Server Elevation of Privilege VulnerabilityCVE-2021-33779Windows AD FS Security Feature Bypass VulnerabilityPatch this cycle
No known exploitation yet, but network-reachable and high impact.
CVE-2021-34458Windows Kernel Remote Code Execution VulnerabilityCVE-2021-34494Windows DNS Server Remote Code Execution VulnerabilityCVE-2021-34450Windows Hyper-V Remote Code Execution VulnerabilitySee all 13 Critical →Most roundups quote a single number. These are three unrelated release streams.
Microsoft channel only · 120 CVEs
| Critical | 13 |
|---|---|
| Important | 105 |
| Moderate | 2 |
| Low | 0 |
What an attacker gains if it works
| Remote Code Execution | 46 |
|---|---|
| Elevation of Privilege | 33 |
| Information Disclosure | 14 |
| Denial of Service | 11 |
| Spoofing | 8 |
| Security Feature Bypass | 8 |
Where this month’s fixes concentrate - filter by any of them in the table below
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-2021-34527 | Windows Print Spooler Remote Code Execution Vulnerability | RCE | 8.8 | ExploitedDisclosed | Windows Print Spooler Components | 5004945 +16 |
| Critical | CVE-2021-34448 | Scripting Engine Memory Corruption Vulnerability | RCE | 6.8 | Exploited | Microsoft Scripting Engine | 5004237 +8 |
| Important | CVE-2021-31979 | Windows Kernel Elevation of Privilege Vulnerability | EoP | 7.8 | Exploited | Windows Kernel | 5004237 +12 |
| Important | CVE-2021-33771 | Windows Kernel Elevation of Privilege Vulnerability | EoP | 7.8 | Exploited | Windows Kernel | 5004237 +6 |
| Critical | CVE-2021-34473 | Microsoft Exchange Server Remote Code Execution Vulnerability | RCE | 9.1 | DisclosedMore likely | Microsoft Exchange Server | 5001779 |
| Important | CVE-2021-34481 | Windows Print Spooler Remote Code Execution Vulnerability | RCE | 8.8 | DisclosedMore likely | Windows Print Spooler Components | 5005030 +12 |
| Important | CVE-2021-36934 | Windows Elevation of Privilege Vulnerability | EoP | 7.8 | DisclosedMore likely | Microsoft Windows | 5005030 +2 |
| Important | CVE-2021-34523 | Microsoft Exchange Server Elevation of Privilege Vulnerability | EoP | 9.0 | Disclosed | Microsoft Exchange Server | 5001779 |
| Important | CVE-2021-33779 | Windows AD FS Security Feature Bypass Vulnerability | Bypass | 8.1 | Disclosed | Active Directory Federation Services (AD FS) | 5004237 +2 |
| Important | CVE-2021-33781 | Azure AD Security Feature Bypass Vulnerability | Bypass | 8.1 | Disclosed | Windows Active Directory | 5004237 +4 |
| Important | CVE-2021-34492 | Windows Certificate Spoofing Vulnerability | Spoofing | 8.1 | Disclosed | Windows PFX Encryption | 5004237 +12 |
| Moderate | ADV210003 | Mitigating NTLM Relay Attacks on Active Directory Certificate Services (AD CS) | Spoofing | - | Disclosed | Windows NTLM | — |
| Important | CVE-2021-33780 | Windows DNS Server Remote Code Execution Vulnerability | RCE | 8.8 | More likely | Role: DNS Server | 5004237 +10 |
| Important | CVE-2021-34520 | Microsoft SharePoint Server Remote Code Execution Vulnerability | RCE | 8.1 | More likely | Microsoft Office SharePoint | 5001975 +2 |
| Important | CVE-2021-34467 | Microsoft SharePoint Server Remote Code Execution Vulnerability | RCE | 7.1 | More likely | Microsoft Office SharePoint | 5001975 +2 |
| Important | CVE-2021-34468 | Microsoft SharePoint Server Remote Code Execution Vulnerability | RCE | 7.1 | More likely | Microsoft Office SharePoint | 5001975 +2 |
| Important | CVE-2021-34449 | Win32k Elevation of Privilege Vulnerability | EoP | 7.0 | More likely | Windows Win32K | 5004237 +2 |
| Critical | CVE-2021-34458 | Windows Kernel Remote Code Execution Vulnerability | RCE | 9.9 | — | Windows Kernel | 5004237 +2 |
| Critical | CVE-2021-34494 | Windows DNS Server Remote Code Execution Vulnerability | RCE | 8.8 | — | Role: DNS Server | 5004237 +10 |
| Critical | CVE-2021-34450 | Windows Hyper-V Remote Code Execution Vulnerability | RCE | 8.5 | — | Role: Windows Hyper-V | 5004237 +2 |
| Critical | CVE-2021-34474 | Microsoft Dynamics 365 Business Central Remote Code Execution Vulnerability | RCE | 8.0 | — | Dynamics Business Central Control | 5004715 +2 |
| Critical | CVE-2021-33740 | Windows Media Remote Code Execution Vulnerability | RCE | 7.8 | — | Microsoft Windows Codecs Library | 5004237 +2 |
| Critical | CVE-2021-34439 | Microsoft Windows Media Foundation Remote Code Execution Vulnerability | RCE | 7.8 | — | Microsoft Windows Media Foundation | 5004238 +1 |
| Critical | CVE-2021-34464 | Microsoft Defender Remote Code Execution Vulnerability | RCE | 7.8 | — | Microsoft Defender | — |
| Critical | CVE-2021-34503 | Microsoft Windows Media Foundation Remote Code Execution Vulnerability | RCE | 7.8 | — | Microsoft Windows Media Foundation | 5004244 +1 |
The same five steps every month, in the order that reduces risk fastest.
CVE-2021-34527 is rated Critical and scores 8.8 - 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? →This release means 78 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 →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 →34 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 →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 78 KB articles across every endpoint, staging them in rings, verifying installed state and producing the compliance evidence. See patch management →
Every month Microsoft has published back to January 2016, each with the same breakdown and the full CVE list.
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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 120 vulnerabilities in July 2021, across Windows, Microsoft Office, Server Software and Developer Tools. 13 are rated Critical, 9 were publicly disclosed before the patch shipped, and 4 were already being exploited. Note that Microsoft's release document lists 189 entries in total, but 35 of those are Azure Linux package updates and 34 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 34 Edge entries alongside Microsoft product fixes would inflate the headline number and imply work for your Windows Update rings that does not exist.
