Critical Microsoft SharePoint Vulnerability: What Small Business Owners Must Do Now
If your small business uses Microsoft SharePoint for document management and collaboration, you need to pay attention. A critical deserialization vulnerability, identified as CVE-2026-58644, was added to the CISA Known Exploited Vulnerabilities catalog on July 16, 2026—and attackers are actively exploiting it right now. This isn't a theoretical threat; it's actively being weaponized in the wild. If you haven't patched your systems yet, your business is at serious risk.
Understanding the Vulnerability in Plain English
SharePoint's deserialization vulnerability is a flaw in how the software processes data from untrusted sources. When SharePoint receives specially crafted data from an attacker, it blindly trusts and processes that data without proper validation. This allows an unauthorized attacker to execute malicious code directly on your server over the network—without needing valid credentials or your permission.
Think of it like this: someone sends your receptionist an official-looking letter claiming to be from your bank. She opens it without checking the sender's address, and suddenly someone with access to your building is walking through your doors. That's essentially what this vulnerability allows attackers to do with your SharePoint servers.
For small business owners, the consequences are severe. An attacker could steal confidential documents, install ransomware, compromise customer data, or use your infrastructure to launch attacks on other organizations. Your business continuity, reputation, and legal liability are all on the line.
Three Critical Action Steps You Must Take
1. Audit Your SharePoint Deployment Today
First, identify every instance of Microsoft SharePoint in your organization. This includes on-premises servers and cloud-based SharePoint Online environments. Document which versions you're running and which systems are exposed to the internet. Many small businesses don't realize they have multiple SharePoint installations across different departments. Create a complete inventory—this is your foundation for response.
2. Apply Security Updates Immediately
Microsoft has released patches for this vulnerability. Follow CISA's BOD 26-04 guidance for prioritizing security updates based on risk. If your SharePoint instance is internet-facing, it should be your highest priority. Apply patches to all affected systems according to vendor instructions. If you're using SharePoint Online through Microsoft 365, Microsoft typically applies patches automatically, but verify your cloud configuration matches security best practices.
3. Evaluate Internet Exposure and Implement Defense Layers
Assess whether your SharePoint systems need to be directly accessible from the internet. If they do, implement additional security controls: network segmentation, web application firewalls, multi-factor authentication, and intrusion detection systems. If mitigations are unavailable for your SharePoint version, consider discontinuing use of the product and migrating to a supported alternative. Your security posture depends on making this decision intentionally, not by default.
Protect Your Business with the Right Tools
Responding to vulnerabilities effectively requires the right toolkit. Malwarebytes provides threat detection and response capabilities to identify if attackers have already exploited this vulnerability in your environment. For protecting your administrative accounts and credentials across your security team, LastPass ensures that even if one system is compromised, your credentials remain secure.
Want to defend against this? Train your skills on Pluralsight's free trial for individuals to deepen your understanding of vulnerability management and secure infrastructure practices. If you're leading security efforts at your organization, Pluralsight for Teams offers comprehensive training for security leaders and your entire team.
The Bottom Line
CVE-2026-58644 is actively being exploited. The deadline for mitigation is July 19, 2026. Every day without patching is a day your business remains vulnerable. Take these three steps now, implement layered security controls, and don't let your small business become another victim of an avoidable breach.