SharePoint CVE-2025-53770: Critical Vulnerability Exposes Enterprises—Learn What Microsoft’s Official Guidance Says

Microsoft officially disclosed a critical security vulnerability—CVE-2025-53770—affecting on-premises SharePoint Server deployments, shaking the foundation of enterprise collaboration infrastructure worldwide. The flaw grants unauthenticated attackers the potential to completely compromise vulnerable servers, highlighting the urgent need for decisive remediation—especially for organizations relying on SharePoint Server 2016, 2019, and Subscription Edition (SE).

What Makes CVE-2025-53770 So Dangerous?

CVE-2025-53770 is not a standalone bug, but the result of chaining two severe security weaknesses:

• CVE-2025-49706 – Authentication Bypass

• CVE-2025-49704 – Deserialization Vulnerability

By cleverly linking these CVEs, attackers can access SharePoint servers without authentication, bypass critical controls, and execute arbitrary C# code—often with high-level privileges.

Which Versions Are At Risk?

• SharePoint Server 2016, 2019, Subscription Edition: Patches are available.

• SharePoint Server 2010, 2013: Out of support, no security update, leaving them dangerously exposed.

Technical Breakdown: The Anatomy of the Attack Chain

The 2025 disclosure reveals a sophisticated exploitation sequence, summarized as:

Step 1: Authentication Bypass (CVE-2025-49706)

• The attacker submits a specially crafted POST request to /layouts/15/ToolPane.aspx?DisplayMode=Edit&a=/ToolPane.aspx with a malicious Referer header, such as /_layouts/SignOut.aspx. This tricks SharePoint into accepting the request as legitimate.

Step 2: Deserialization Attack (CVE-2025-49704)

• The next request uses a serialized payload in spinstall0.aspx to extract cryptographic MachineKey values from the server’s web.config file.

Step 3: Remote Code Execution

• Armed with these keys, the criminal crafts a C# code payload within a valid __VIEWSTATE token. SharePoint trusts and executes this code, fully compromising the system.

Risks:

• Complete server compromise

• Lateral movement and data theft

• Persistent backdoor for future attacks

Microsoft’s Official Guidance: How to Protect Your SharePoint Servers

1. Apply Security Updates—Immediately

Microsoft’s Security Response Center and the Azure Network Security Blog strongly recommend patching all affected SharePoint 2016, 2019, and SE servers without delay.

• Locate and apply the latest security updates through the MSRC or within your organization’s update management system.

• Restart servers to complete the process fully.

2. Mitigate at the Network Level: Protect Legacy Systems

• SharePoint 2010 and 2013 will NOT receive security patches. If migration is not immediately feasible, restrict network access to these servers or disable their use entirely to reduce exposure.

3. Deploy Azure Web Application Firewall (WAF) Protections

Microsoft provides step-by-step guidance for using Azure WAF to block and monitor suspicious activity targeting vulnerable endpoints.

How to Create a Custom Rule in Azure WAF:

• Condition 1: URI contains /layouts/15/ToolPane.aspx or /layouts/15/spinstall0.aspx

• Condition 2: Referer header contains /layouts/SignOut.aspx or /layouts/15/SignOut.aspx

Example WAF Custom Rule (JSON):

This custom rule blocks both typical and obfuscated attacks, providing an additional protective layer.

• For step-by-step instructions, visit the Azure docs on custom WAF rules for Application Gateway and Azure Front Door.

Immediate Actions for IT & Security Teams

• Inventory all on-premises SharePoint servers. Identify versions and patch compliance.

• Prioritize patching for supported editions (2016, 2019, SE).

• Restrict legacy access or segment network zones for unsupported versions.

• Enable Azure WAF (if using Application Gateway or Front Door) and deploy targeted custom rules.

• Monitor for any suspicious requests or abnormal traffic patterns.

• Engage incident response if exploitation is suspected.

Why Does This Matter for Your Organization?

With SharePoint still a backbone for secure document management, internal portals, and business process automation, a breach could result in:

• IP theft, regulatory violations, and operational shut-down

• Lateral network penetration (pivoting to other assets)

• Reputational damage with customers and partners

Attackers continue to develop new variants and evasion tactics. As we saw with the recent Exchange vulnerability, patching alone isn’t enough—holistic defense using advanced tools like Azure WAF and clear internal processes is crucial for enterprise resilience.