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Microsoft Patches Six Actively Exploited Zero-Days in February 2026, Matching Last Year's Record High

Microsoft's February Patch Tuesday fixes 58 flaws including six zero-days already under attack, with CISA ordering immediate federal remediation.

Cybersecurity Vulnerabilities
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Overview

Microsoft’s February 2026 Patch Tuesday, released on February 10, addresses 58 security vulnerabilities across Windows, Office, Azure, and developer tools. Six of those flaws were already being exploited in the wild at the time of disclosure, according to BleepingComputer. That figure matches the single-month record set in March 2025, as noted by CyberScoop, and CISA has added all six to its Known Exploited Vulnerabilities catalog.

“The number of bugs under active attack is extraordinarily high,” said Dustin Childs of the Trend Micro Zero Day Initiative, as quoted by CyberScoop.

The Six Zero-Days

Three of the actively exploited vulnerabilities are security feature bypasses that share what Satnam Narang of Tenable called “strong similarities” in how they undermine protections against malicious files:

  • CVE-2026-21510 (CVSS 8.8) — A Windows Shell flaw that allows attackers to circumvent SmartScreen and similar security prompts once a user clicks a specially crafted link or shortcut file. It was publicly disclosed before the patch, according to Tenable.

  • CVE-2026-21513 (CVSS 8.8) — A bypass in the MSHTML framework, the rendering engine inherited from Internet Explorer, that weakens browser and Office sandbox protections. Per Malwarebytes, the flaw requires victims to open malicious HTML files or crafted shortcuts and was both publicly disclosed and exploited before a fix was available.

  • CVE-2026-21514 (CVSS 7.8) — A Microsoft Word vulnerability that bypasses OLE mitigations in Microsoft 365 and Office. An attacker must convince a target to open a malicious document, though the Preview Pane is not an attack vector, according to Tenable.

The remaining three zero-days target different attack surfaces:

  • CVE-2026-21519 (CVSS 7.8) — A type confusion flaw in the Desktop Window Manager that grants SYSTEM-level privileges to a local authenticated attacker, according to Malwarebytes.

  • CVE-2026-21533 (CVSS 7.8) — An elevation of privilege bug in Windows Remote Desktop Services. As reported by BleepingComputer, the exploit binary modifies a service configuration key to place attacker-controlled accounts into the Administrators group. CrowdStrike Intelligence has observed threat actors using this binary against U.S.- and Canada-based entities since at least December 2025.

  • CVE-2026-21525 (CVSS 6.2) — A null pointer dereference in the Windows Remote Access Connection Manager (RasMan) that allows an unauthenticated local attacker to crash the service, as detailed by Malwarebytes.

Broader Patch Scope

Beyond the zero-days, the February release includes five Critical-rated vulnerabilities and dozens of Important-rated fixes. According to BleepingComputer, the full breakdown by vulnerability type is:

  • 25 Elevation of Privilege
  • 12 Remote Code Execution
  • 7 Spoofing
  • 6 Information Disclosure
  • 5 Security Feature Bypass
  • 3 Denial of Service

Notable non-zero-day flaws include CVE-2026-21511, an Outlook spoofing vulnerability (CVSS 7.5) where crafted emails trigger untrusted data deserialization — and unlike many Office bugs, the Preview Pane is an attack vector, according to Tenable.

What We Don’t Know

  • Microsoft has not attributed the zero-day exploitation to specific threat actors beyond CrowdStrike’s reporting on CVE-2026-21533. The identity of attackers leveraging the other five zero-days remains undisclosed.
  • The full scope of in-the-wild exploitation — including how many organizations were compromised before patches became available — has not been quantified.
  • Whether the three related security feature bypasses (CVE-2026-21510, -21513, -21514) were exploited as part of coordinated campaigns or independently is unclear.

What Comes Next

With CISA’s addition of all six zero-days to its Known Exploited Vulnerabilities catalog, U.S. federal agencies face mandatory remediation deadlines. Enterprise security teams are advised to prioritize the two CVSS 8.8 flaws — the Windows Shell and MSHTML bypasses — given their network-based attack vectors and the fact that both were publicly known before patches shipped.