A newly discovered critical vulnerability in Microsoft SharePoint has triggered a cybersecurity scare across the world. This high-severity flaw, unearthed in mid-July 2025, has already been exploited in the wild and is actively being used by threat actors to breach organizations using vulnerable, on-premises SharePoint Servers.
In this article, we’ll break down everything you need to know about the SharePoint vulnerability (CVE-2025-53770)—from how it works, the systems it affects, to the steps your team should take immediately to stay secure.
What Is Microsoft SharePoint and Why Is It at Risk?
SharePoint is Microsoft’s enterprise-grade collaboration and document management platform, used by corporations, government agencies, healthcare providers, and educational institutions. It’s a vital tool that stores sensitive documents, communication workflows, and internal data. Because of its widespread use and integration into thousands of enterprise environments, SharePoint is a prime target for cybercriminals. When a zero-day flaw is discovered, bad actors race to exploit it before patches are released or systems are updated.
What Happened in July 2025?
Cybersecurity researchers from Viettel Cyber Security and Trend Micro’s Zero Day Initiative (ZDI) revealed that attackers had started actively exploiting a previously unknown bug in SharePoint. The issue, designated CVE-2025-53770, allowed attackers to execute arbitrary code remotely—giving them full access to the affected server. What’s particularly alarming: this exploit does not require authentication. In other words, no login credentials are needed for an attacker to gain a foothold.
Real-Time Exploitation
Security teams around the globe began picking up on abnormal activity as early as July 18, 2025. Attackers targeted vulnerable servers at scale, focusing on systems that were directly exposed to the internet.
Understanding CVE-2025-53770: How the Vulnerability Works
This vulnerability leverages a technique known as “deserialization of untrusted data.” Attackers send malicious payloads that trigger SharePoint’s server to interpret these payloads as trusted code. Once executed, attackers can install backdoors, information stealers, and web shells—granting them indefinite access to the compromised systems.
CVSS Score: Critical
Microsoft ranked this flaw as 9.8 out of 10 on the CVSS scale, highlighting the urgent risk it poses. This puts it among the most severe vulnerabilities identified this year.
Which SharePoint Systems Are Affected?
It’s crucial to note that only on-premises versions of SharePoint are impacted. Cloud-based SharePoint Online (part of Microsoft 365) is unaffected.
Vulnerable Versions:
- Microsoft SharePoint Server 2016
- Microsoft SharePoint Server 2019
- SharePoint Server Subscription Edition (SE)
Who’s Been Hit? Real-World Impact
Several major security agencies, including CISA, FBI, and Canada’s CCCS, confirmed widespread exploitation. Targets included:
- U.S. federal and state agencies
- Public infrastructure providers
- Financial and legal firms
- Universities and research institutions
Some organizations even discovered that sensitive data—including regulatory documents and internal files—had already been accessed by unauthorized parties.
Microsoft’s Emergency Response and Patch Status
As soon as the attacks were confirmed, Microsoft worked rapidly to deliver emergency fixes. Here’s where we currently stand:
Security Updates Available:
- SharePoint Server Subscription Edition: Patched (Update KB5002768)
- SharePoint Server 2019: Patched (Update KB5002741)
- SharePoint Server 2016: No official patch yet as of writing. Microsoft has recommended isolation and monitoring until a fix is released.
Microsoft also published specific mitigation guidance for SharePoint 2016 users, urging them to restrict internet access to vulnerable servers and rotate server-side crypto keys (MachineKeys).
Immediate Actions to Secure Your Systems
If your organization manages a SharePoint server on-premises, here are the top defensive measures you should apply right now:
✅ 1. Patch Systems Immediately
Install the latest Microsoft security update relevant to your SharePoint version. If you’re using SharePoint SE or 2019, the fixes are live now. Windows Server Update Services (WSUS) or manual installers can be used.
✅ 2. Isolate Vulnerable Servers
If using SharePoint 2016, temporarily cut off internet-facing access. Unpatched servers are sitting ducks for attackers.
✅ 3. Rotate MachineKeys
MachineKey values are critical for security in ASP.NET-based apps like SharePoint. Reset them to prevent attackers from forging server-trusted tokens.
✅ 4. Enable AMSI & Defender
Microsoft recommends enabling the Antimalware Scan Interface (AMSI) and deploying Microsoft Defender for Endpoint to detect exploit activity in real-time.
✅ 5. Scan for Web Shells
Use forensic tools or Defender’s file-scanning capabilities to inspect your servers for malicious ASPX files or unauthorized shell scripts.
The Human Side: Companies Scrambling to Respond In many IT departments, the following days were described as “chaotic,” with round-the-clock shifts to secure data and report findings to management. A cybersecurity lead at a U.K.-based healthcare provider said:
“When the alert came in over the weekend, our entire security operations center sprang into action. We chose to take our systems down temporarily. Better safe than sorry when patient medical data is involved.”
Long-Term Lessons for Organizations:
This isn’t the first time SharePoint has faced security risks, but it serves as a vital reminder of the ongoing cybersecurity arms race. Here’s what this incident teaches us:
- Legacy Systems Are Risky: Organizations still using older versions like SharePoint 2016 will continue to face delays in support.
- Zero-Days Can Cost Millions: Between downtime, data loss, and brand damage, even a brief window of exposure can be costly.
- Proactive Monitoring is Critical: A firewall alone isn’t enough. Real-time threat detection makes all the difference.
- Cloud Migration May Be Safer: While not immune, Microsoft’s cloud-based services benefit from faster patch cycles and 24/7 monitoring by Microsoft’s security teams.
Frequently Asked Questions
Q: Is SharePoint Online affected?
A: No. This vulnerability only impacts self-hosted SharePoint server installations. If you use Microsoft 365, you are not at risk from CVE-2025-53770.
Q: What if I can’t patch my SharePoint 2016 server yet?
A: Disconnect it from the network, limit user access, rotate your MachineKeys, and closely monitor all file activities.
Q: How do I know if we’ve been breached?
Check for unfamiliar PowerShell logs, unauthorized changes to SharePoint pages, malicious files (.ASPX, .DLL, or .EXE) in the root directory, or unusual authentication activity.
Summary Table
| Key Detail | Description |
|---|---|
| Vulnerability ID | CVE-2025-53770 |
| Date Disclosed | July 18, 2025 |
| Affected Products | SharePoint Server 2016, 2019, Subscription Edition |
| Attack Method | Deserialization of Untrusted Data → Remote Code Execution |
| CVSS Score | 9.8 (Critical) |
| Patches Available? | Yes (except for SharePoint 2016) |
| Affected Systems | On-prem SharePoint Servers (not SharePoint Online) |
| Recommendations | Patch, rotate keys, inspect for web shells, isolate 2016 |
Final Thoughts
The July 2025 Microsoft SharePoint vulnerability is a glaring example of how even the most trusted enterprise software can become a gateway for cyberattacks with global consequences. Organizations that deploy on-premise solutions must remain vigilant, agile, and proactive in their response strategies. Whether you’re a small firm or a federal agency, the takeaway is the same: patch fast, monitor continuously, and treat every zero-day like it’s already knocking at your door.
