By Sergiu Gatlan
Publication Date: 2026-01-26 18:20:00
Microsoft has released emergency out-of-band security updates to patch a high-severity Microsoft Office zero-day vulnerability exploited in attacks.
The security feature bypass vulnerability, tracked as CVE-2026-21509, affects multiple Office versions, including Microsoft Office 2016, Microsoft Office 2019, Microsoft Office LTSC 2021, Microsoft Office LTSC 2024, and Microsoft 365 Apps for Enterprise (the company’s cloud-based subscription service).
However, as noted in today’s advisory, security updates for Microsoft Office 2016 and 2019 are not yet available and will be released as soon as possible.
While the preview pane is not an attack vector, unauthenticated local attackers can still successfully exploit the vulnerability through low-complexity attacks that require user interaction.
“Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally. An attacker must send a user a…
