Critical Microsoft SharePoint Vulnerability: CVE-2025-53770 Explained

Microsoft SharePoint is widely utilized across industries and government sectors for its collaboration and document management capabilities, making it a critical component of many organizational IT infrastructures. However, a newly identified vulnerability, CVE-2025-53770, has posed a significant threat to SharePoint servers, allowing attackers to remotely execute harmful code without any prior authentication. Given the severity and the ongoing active exploitation of this issue, it’s crucial for organizations to understand the risk and swiftly implement necessary measures.

Understanding the Vulnerability

CVE-2025-53770 is a critical security flaw identified in on-premises Microsoft SharePoint Server installations. The vulnerability arises from improper handling (deserialization) of untrusted data. It allows attackers to remotely execute malicious code without requiring any authentication. Attackers exploit this vulnerability by sending specially crafted requests, targeting the /ToolPane.aspx endpoint and using a spoofed Referer header.

Initially linked to the "ToolShell exploit chain," this vulnerability has evolved, bypassing previous security fixes and is actively being exploited.

Who Is Affected and How Serious Is It?

• Affected Versions: SharePoint Server 2016, 2019, and Subscription Edition (on-premises only).
• Not Affected: SharePoint Online (Microsoft 365).
• Impact Scope: Several government agencies, educational institutions, and corporate entities worldwide are affected. Over 75 confirmed breaches have occurred, potentially placing tens of thousands of servers at risk.

Attackers exploiting CVE-2025-53770 can:

• Execute remote commands on compromised servers.
• Steal cryptographic keys (MachineKeys), allowing continuous access even after servers are patched.
• Move laterally across connected Microsoft services such as Outlook, Teams, and OneDrive.

Due to its active exploitation, prompt action is essential.

Potential Impacts

• Remote Code Execution: Full server compromise without authentication.
• Persistent Access: Attackers maintain server access post-patch through stolen keys.
• Data Compromise: Potential for data theft, manipulation, or deletion.
• Extended Risk: Compromise could spread to other integrated Microsoft services.

How to Mitigate and Recover from CVE-2025-53770

Immediate actions include:

1. Patch Your SharePoint Servers Immediately
   • Microsoft released patches for SharePoint 2019 and Subscription Edition in July 2025.
   • Patch release for SharePoint 2016 is forthcoming; monitor official Microsoft channels for updates.
2. Enable Enhanced Protection Measures
   • Activate AMSI (Antimalware Scan Interface).
   • Deploy Microsoft Defender Antivirus or similar solutions on all servers.
3. Rotate Security Keys
   • Change your SharePoint Server ASP.NET MachineKeys immediately after patching.
4. Network Access Control
   • Temporarily isolate or limit access to your SharePoint servers from external networks.
   • Restrict server access to only trusted IP addresses.
5. Monitoring and Threat Detection
   • Closely monitor network traffic, especially suspicious POST requests to /_layouts/15/ToolPane.aspx?DisplayMode=Edit.
   • Implement network defenses, such as Web Application Firewalls (WAF) and Intrusion Prevention Systems (IPS).
6. Conduct Post-Incident Audits
   • Thoroughly investigate for possible backdoors, unusual activity in IIS processes, or unauthorized changes.
7. Threat Intelligence and Scanning
   • Use vulnerability scanning tools (like Qualys) to detect this vulnerability and potential compromises.
8. Report Incidents Promptly
   • If compromised, report to cybersecurity authorities such as CISA immediately.

CVE-2025-53770 represents an urgent and critical risk for organizations using affected SharePoint servers. Immediate patching, monitoring, and implementing security measures are essential to mitigate this threat.

For the latest updates and detailed guidance, check the following sources:

• Microsoft - Keep checking as guidance may continue to be updated.
• CISA -Report if it has been found your systems are compromised.
• Eye Security - Identified large scale exploitation of this zero-day.

Stay informed and take swift, appropriate actions to protect your systems.

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