CVE-2026-21509—Microsoft Office Security Feature Bypass Vulnerability

Vulnerability Name

Microsoft Office Security Feature Bypass Vulnerability

Description

Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

Known To Be Used in Ransomware Campaigns?

Ransomware Status:

Unknown

Action

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Additional Notes

• Please adhere to Microsoft’s recommended guidelines to address this vulnerability. Implement all final mitigations provided by the vendor for Office 2021, and apply the interim corresponding mitigations for Office 2016 and Office 2019 until the final patch becomes available. For more information please see: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509
• https://nvd.nist.gov/vuln/detail/CVE-2026-21509

Related News Articles

• Gamaredon Exploits WinRAR to Deliver GammaWorm and GammaSteel Against UkraineJune 2, 2026
• APT28 Deploys PRISMEX Malware in Campaign Targeting Ukraine and NATO AlliesApril 8, 2026
• APT28 hackers deploy customized variant of Covenant open-source toolMarch 10, 2026
• APT28 Tied to CVE-2026-21513 MSHTML 0-Day Exploited Before Feb 2026 Patch TuesdayMarch 2, 2026
• Russian hackers are exploiting recently patched Microsoft Office vulnerability (CVE-2026-21509)February 3, 2026

Related Weaknesses

• CWE-807