Does Visio Heap Overflow CVE-2026-102856 Expose Enterprise Environments?

The short version

• An unauthenticated attacker can execute code over a network via a heap overflow in Visio.
• Affected software includes Microsoft 365 Apps for Enterprise, Office LTSC 2021, and LTSC 2024.
• Specific version thresholds are defined for LTSC 2021 and LTSC 2024 builds in the advisory.

The details

Microsoft has identified a remote code execution vulnerability in Microsoft Office Visio, designated as CVE-2026-102856. According to the official security update guide, the flaw stems from a heap-based buffer overflow that allows an unauthorised attacker to execute code over a network. The National Vulnerability Database records the Common Vulnerability Scoring System rating as 8.8, classifying the severity as high. The weakness is linked to CWE-122 and CWE-190.

This issue impacts organisations running Microsoft 365 Apps for Enterprise that have not received the latest releases. It also affects those using Microsoft Office LTSC 2021 prior to build 16.0.14334.20974 and Microsoft Office LTSC 2024 before build 16.0.17932.21056. Users of these specific older builds remain exposed until they apply the necessary updates.

The context

This disclosure follows a pattern of critical flaws in Microsoft software. As Honeypot Daily reported on 2026-10-14, a critical remote code execution vulnerability was found in the Windows CCFFilter Driver. That same day, reporting highlighted a command injection flaw in the Python thumbnail library. These incidents underscore the persistent risk to enterprise environments relying on widely deployed software stacks that require regular patching to mitigate remote execution risks.

Next steps

Organisations should verify their current Visio versions against the affected build numbers listed in the Microsoft advisory. Teams must ensure that Microsoft 365 Apps for Enterprise are configured to receive automatic security updates. For LTSC deployments, administrators need to manually check and apply the specific cumulative updates that address this heap overflow vulnerability to close the exposure window.

What defenders should look for

Security operations teams should monitor for unusual process creation events originating from Visio executables. Check whether any Visio instances are attempting to connect to external command and control infrastructure. Look for anomalous network traffic patterns that deviate from standard document processing behaviour. If suspicious activity is detected, isolate the affected endpoints immediately to prevent lateral movement. Review logs for any unauthorised script execution that follows the opening of a Visio file.

What to do and how to stay safe: Microsoft

• Audit your environment to identify all endpoints running affected versions of Visio.
• Ensure Microsoft 365 Apps are set to update automatically to receive the latest security patches.
• For LTSC versions, manually verify that the specific build numbers mentioned in the advisory are installed.
• Monitor network logs for unusual outbound connections from workstations running Visio.

Step-by-step guide: How Virtual Patching Works: The Mechanics Behind Inline Protection

General security guidance from the Honeypot Daily newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

What is the CVSS score for CVE-2026-102856?

The CVSS score is 8.8, which is rated as high severity.

Which Visio versions are affected by this vulnerability?

Microsoft 365 Apps for Enterprise, Office LTSC 2021 before 16.0.14334.20974, and LTSC 2024 before 16.0.17932.21056 are affected.

Can an attacker exploit this flaw remotely?

Yes, the advisory states that an unauthorised attacker can execute code over a network.