REDMOND, Wash. – July 21, 2025 – Microsoft has rushed out an emergency security update to address a critical vulnerability in its widely used SharePoint Server and SharePoint Online platforms. The flaw, tracked as CVE-2025-53770, could allow attackers to remotely execute malicious code on affected systems, potentially granting them full control over SharePoint environments and access to sensitive data.
The vulnerability, classified as Critical with a CVSS score of 9.8 out of 10, involves improper handling of specially crafted web requests. Security researchers warn that exploitation requires no authentication or user interaction, making it particularly dangerous. An attacker could exploit the flaw simply by sending a malicious network packet to a vulnerable SharePoint server.
"SharePoint Under Siege"
The vulnerability was discovered and reported by researchers at Eye Security. Their initial findings, detailed in a blog post titled "SharePoint Under Siege: Analyzing CVE-2025-53770", highlighted the potential for widespread compromise. The researchers demonstrated how the flaw could be leveraged to bypass security mechanisms and execute arbitrary commands with elevated privileges.
"Given SharePoint's central role in document management, collaboration, and often internal workflows for countless organizations, a vulnerability of this magnitude is a prime target for both ransomware groups and state-sponsored actors," stated Lena Torres, Lead Security Analyst at Eye Security. "The potential impact on confidentiality, integrity, and availability is severe."
Microsoft Issues Urgent Guidance
Microsoft confirmed active, targeted exploitation attempts occurring in the wild shortly before releasing the patch. In response, they issued an out-of-band security update, bypassing the usual Patch Tuesday schedule, emphasizing the severity.
"The Microsoft Security Response Center (MSRC) is aware of limited targeted attacks leveraging CVE-2025-53770," the company stated in its official security advisory. "We strongly recommend customers apply the updates immediately to protect their environments. This update addresses the vulnerability by correcting how SharePoint handles specific types of requests."
The advisory provides detailed information on affected versions (including multiple SharePoint Server 2019, 2016, Subscription Edition, and SharePoint Online) and step-by-step patching instructions. Microsoft emphasizes that SharePoint Online customers are protected automatically and require no action beyond verifying service health.
CISA Sounds the Alarm
The US Cybersecurity and Infrastructure Security Agency (CISA) quickly added CVE-2025-53770 to its Known Exploited Vulnerabilities (KEV) Catalog, mandating federal civilian agencies to patch by August 4th, 2025. However, CISA strongly urged all organizations to prioritize patching.
In its alert, CISA reiterated the critical nature of the flaw: "Successful exploitation of this vulnerability could allow an unauthenticated attacker to execute arbitrary code on an affected SharePoint Server. This could lead to a complete compromise of the system, data theft, deployment of ransomware, or further network propagation."
Action Required: Patch Immediately
Security experts unanimously agree that applying the patch is the only effective mitigation. Organizations running on-premises SharePoint Server should:
- Identify Affected Systems: Review Microsoft's advisory to confirm which SharePoint versions and builds are vulnerable.
- Apply the Emergency Update: Download and install the patches provided by Microsoft without delay. Test in non-production environments first if possible, but expedite deployment.
- Monitor for Compromise: Review server logs for any suspicious activity preceding the patch, especially unexpected processes or connections.
- Verify SharePoint Online Status: While Microsoft handles patching for the cloud service, administrators should monitor the Microsoft 365 admin portal for any service advisories.
"Patch Now"
The discovery of CVE-2025-53770 and the subsequent emergency response underscore the constant threat facing widely deployed enterprise software like SharePoint. With proof-of-concept exploit code likely circulating and active attacks confirmed, the window for mitigation is narrow. Security teams are advised to treat this patch deployment as their highest priority task. Delaying even by hours could significantly increase the risk of a devastating breach.
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