CVE-2026-102856 – Microsoft Office Visio Remote Code Execution Vulnerability

Microsoft has addressed a Critical Remote Code Execution (RCE) vulnerability in Microsoft Office Visio that could allow an unauthorized attacker to execute malicious code on an affected system. The vulnerability, identified as CVE-2026-102856, results from a heap-based buffer overflow and can be triggered when a user opens a specially crafted Visio file. An attacker does not need existing access or privileges to attempt exploitation, making this a significant security concern. Successful exploitation could compromise sensitive information, allow unauthorized system modifications, or disrupt business operations. Although exploitation is considered less likely and no active exploitation has been reported, the vulnerability’s critical severity makes timely patching essential.

CVSS SCORE: 8.8

SEVERITY: Critical

Threat

This vulnerability creates a serious security risk because attackers could use a malicious Microsoft Visio file to execute unauthorized code on a targeted system.

The attack can be initiated remotely over a network and requires no prior authentication or privileges. However, the attacker must convince a user to open a specially crafted file.

Successful exploitation could allow attackers to:

• Execute malicious code on vulnerable systems.
• Access or steal sensitive business information.
• Modify or damage important files and data.
• Disrupt critical business applications and operations.
• Compromise the confidentiality, integrity, and availability of affected systems.

The vulnerability has low attack complexity, meaning exploitation does not require complicated technical conditions once a victim opens the malicious file.

Exploits

Microsoft has assessed this vulnerability as “Exploitation Less Likely.”

The vulnerability was not publicly disclosed before publication, and there are no reported cases of active exploitation.

The exploit code maturity is classified as Unproven, indicating that a working public exploit has not been confirmed.

The existence of publicly available proof-of-concept (PoC) exploit code cannot be confirmed.

There is also no confirmed evidence that this vulnerability has been exploited as a zero-day.

However, attackers could potentially develop malicious Visio documents designed to exploit the vulnerability.

Technical Summary

CVE-2026-102856 is a heap-based buffer overflow vulnerability (CWE-122) associated with an integer overflow or wraparound weakness (CWE-190) in Microsoft Office Visio.

The vulnerability involves improper handling of memory during the processing of specially crafted content.

An integer overflow can occur when a calculation produces a value outside the supported integer range. This can contribute to incorrect memory handling and potentially lead to a heap-based buffer overflow.

A heap-based buffer overflow occurs when an application writes data beyond the boundaries of an allocated memory region. This can corrupt memory and potentially allow attackers to execute arbitrary code.

An attacker could exploit this weakness by creating a malicious Visio file and persuading a user to open it.

When the vulnerable application processes the specially crafted file, the memory corruption condition could potentially be triggered, resulting in remote code execution.

The vulnerability has the following technical characteristics:

• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: High

Importantly, the Preview Pane is not an attack vector for this vulnerability. The user must open the specially crafted file to trigger the attack.

Successful exploitation could result in unauthorized code execution and potentially compromise the affected system.

Exploitability

The vulnerability affects the following Microsoft products:

• Microsoft 365 Apps for Enterprise (32-bit and 64-bit).
• Microsoft Office LTSC 2021 (32-bit and 64-bit).
• Microsoft Office LTSC 2024 (32-bit and 64-bit).

An attacker could exploit the vulnerability by convincing a user to open a specially crafted Visio file.

No prior privileges are required, but user interaction is necessary.

Microsoft currently rates exploitation as Less Likely.

Business Impact

This vulnerability presents a significant business risk because Microsoft Office applications are commonly used across enterprise environments.

A successful attack could turn an ordinary document-opening activity into a serious security incident.

Sensitive Data Exposure: Attackers could potentially access confidential business documents, financial information, and other sensitive organizational data.

Unauthorized Code Execution: Successful exploitation could allow malicious code to run on affected systems, potentially compromising business applications and information.

Operational Disruption: Exploitation could affect system availability, interrupt employee productivity, and disrupt important business processes.

Financial Consequences: Organizations could face incident response costs, operational downtime, recovery expenses, and potential financial losses.

Reputational Damage: A successful security incident involving sensitive information could damage customer confidence and business relationships.

The vulnerability is particularly concerning because attackers do not require existing system privileges.

A trusted business document could become an entry point for attackers, turning a routine file-opening action into a costly security incident.

Workaround

Microsoft has not identified any official mitigations or workarounds for this vulnerability.

If immediate patch deployment is not possible, organizations should consider the following precautionary measures:

• Avoid opening Visio files from unknown or untrusted sources.
• Restrict access to suspicious or unexpected Visio attachments.
• Educate employees about malicious document-based attacks.
• Monitor endpoints for suspicious Office application activity.
• Prioritize installing the official Microsoft security updates.

These precautions may reduce exposure but do not eliminate the vulnerability.

Urgency

Critical Severity – High Deployment Priority

CVE-2026-102856 requires urgent patch deployment because it allows potential remote code execution with a CVSS score of 8.8.

The vulnerability combines several concerning characteristics:

• Critical severity, with potentially serious consequences for affected systems.
• Low attack complexity, reducing the technical barriers to exploitation.
• No privileges required, allowing unauthorized attackers to attempt exploitation.
• High confidentiality, integrity, and availability impacts, increasing the potential damage from a successful attack.

Although active exploitation has not been reported and Microsoft considers exploitation less likely, the possibility of remote code execution makes this vulnerability a significant enterprise security concern.

Organizations should prioritize updating affected Microsoft 365 Apps and Office LTSC installations, particularly on systems frequently handling documents from external sources.

Delaying this patch leaves a dangerous opening: one malicious document could be enough to compromise a business system.