SharePoint Flaw Under Attack After PoC Release—Are You Protected?

Emily Davis · 2026-07-21

If you're running Microsoft SharePoint Server, you need to pay attention to a critical vulnerability that's now being actively exploited. Security researchers at watchTowr recently confirmed that a third SharePoint Server flaw—patched by Microsoft in the July 2026 Patch Tuesday update—has come under active attack after a public proof-of-concept (PoC) was released. This isn't just another routine patch. The vulnerability, tracked as CVE-2026-50522, carries a CVSS score of 9.8—that's about as critical as it gets. It's a deserialization of untrusted data issue in Microsoft Office SharePoint that could let an unauthenticated attacker execute code remotely over a network. In plain English, it means someone could take over your SharePoint server without needing any credentials at all. ### What Makes This Vulnerability So Dangerous? Think of deserialization like this: when your computer sends data between systems, it often serializes it—turning complex objects into a format that's easy to transport. When the receiving system deserializes that data, it rebuilds the original object. The problem here is that SharePoint doesn't properly validate the data before deserializing it, so an attacker can craft a malicious payload that gets executed on the server. Here's what makes CVE-2026-50522 especially concerning: - No authentication required: The attacker doesn't need a username or password - Remote code execution: They can run any code they want on your server - Network-based attack: They don't need physical access or local privileges - Public PoC available: The exploit code is now public, making it easier for attackers to use Microsoft credited the security team at DEVCORE for discovering this flaw. The company released a patch in July 2026, but if you haven't applied it yet, your system is at risk. ### Why Active Exploitation Matters When a vulnerability is "actively exploited," it means attackers are already using it in the wild. This isn't a theoretical risk or something you can ignore until your next maintenance window. The public PoC makes it even worse, because now even less skilled attackers can use the exploit. Security researchers often debate whether to release PoCs publicly. On one hand, they help defenders test their systems. On the other hand, they give attackers a ready-made weapon. In this case, the damage is already done—the exploit is out there, and you need to act now. ### How to Protect Your SharePoint Environment If you're responsible for a SharePoint deployment, here's what you should do immediately: - Apply the July 2026 Patch Tuesday updates if you haven't already - Check your logs for any signs of unusual activity or unauthorized access - Consider implementing network segmentation to limit exposure - Review your firewall rules to restrict access to SharePoint from untrusted networks - Monitor for any suspicious file uploads or unexpected server behavior The good news is that Microsoft has released a fix. The bad news is that many organizations are slow to apply patches, especially for complex systems like SharePoint that might require testing and downtime. ### The Bigger Picture This is the third SharePoint Server flaw to be exploited after a Patch Tuesday update in recent months. It's a pattern that should concern anyone running this platform. Microsoft has been working hard to secure SharePoint, but the complexity of the software means vulnerabilities will keep appearing. For IT teams, this reinforces a few key lessons: - Patch Tuesday updates should be tested and deployed as quickly as possible - Critical vulnerabilities with public PoCs demand immediate attention - No system is safe if you delay applying security updates - Regular security audits and monitoring are essential If you're still running an unpatched SharePoint Server, consider this your wake-up call. The attackers aren't waiting, and neither should you.