Critical Microsoft SharePoint Vulnerability: What Small Business Owners Need to Know Now

If your small business uses Microsoft SharePoint Server to store files, manage projects, or collaborate with your team, you need to read this. A serious security vulnerability has been discovered that could allow attackers to take control of your system—and you have until July 4, 2026 to fix it. This isn’t something to ignore. Here’s what you need to know and what you must do to protect your business.

Understanding the SharePoint Deserialization Vulnerability

Microsoft SharePoint Server contains what’s called a “deserialization of untrusted data” vulnerability. In plain English, this means that SharePoint can be tricked into running malicious code if an attacker who has some level of access sends it specially crafted data. Think of it like giving someone a locked box with instructions inside—if those instructions are malicious, bad things happen.

The critical part: an authorized attacker (someone with at least some legitimate access to your system) could exploit this vulnerability to execute code remotely across your network. This could lead to data theft, system compromise, or complete business disruption. For small businesses without large IT teams, this kind of attack could be catastrophic.

Why This Matters for Your Business

SharePoint is commonly used by small and medium-sized businesses to store important documents, manage workflows, and enable team collaboration. If compromised, attackers could access confidential client information, financial records, intellectual property, or employee data. The damage extends beyond data loss—it includes regulatory fines, lost customer trust, and operational downtime.

The fact that an “authorized attacker” is required doesn’t mean you’re safe. Authorized access could come from a disgruntled employee, a compromised contractor account, or someone who gained access through another vulnerability. You must assume this risk exists.

Three Critical Action Steps You Must Take

Step 1: Identify Your SharePoint Infrastructure

First, determine whether your business uses Microsoft SharePoint Server. Check with your IT team or managed service provider. Make a list of all SharePoint instances, their versions, and whether they’re cloud-based or on-premises. Document which departments and systems depend on SharePoint for daily operations.

Step 2: Apply Security Updates Immediately

Microsoft has released patches to fix this vulnerability. Your IT team must apply these updates according to CISA’s BOD 26-04 guidance, which prioritizes security updates based on risk level. Don’t delay—treat this as a high-priority patch. If you use Microsoft’s cloud-based SharePoint through Microsoft 365, Microsoft is handling patches automatically, but verify your tenant is updated.

Step 3: Evaluate Internet Exposure and Access Controls

Review who has authorized access to your SharePoint systems. Implement the principle of least privilege—give employees only the access they actually need. If SharePoint is exposed to the internet, consider whether it needs to be. Implement strong authentication, multi-factor authentication, and network monitoring to detect suspicious activity.

Building a Security-First Culture

This vulnerability is a reminder that cybersecurity isn’t a one-time fix—it’s an ongoing process. Your team needs training to recognize threats and understand security best practices. Want to defend against this? Train your skills on Pluralsight’s free trial to stay current on emerging threats.

Recommended Security Tools

To strengthen your overall security posture, consider these solutions:

• Malwarebytes – Provides malware detection and removal for endpoint protection
• LastPass – Secures passwords and credential management across your organization
• Pluralsight Free Trial – Develop security skills for individuals
• Pluralsight for Teams – Train security leaders and IT teams at scale

Act now. Your deadline is July 4, 2026, but don’t wait. Patch your systems, secure your access controls, and invest in your team’s security knowledge. Your business depends on it.