Introduction to SharePoint RCE Vulnerability
Recent disclosures have brought to light a proof-of-concept (PoC) exploit and intricate technical insights for CVE-2025-53770, a significant remote code execution (RCE) vulnerability affecting on-premises Microsoft SharePoint Server. With these revelations, the likelihood of mass exploitation in environments lacking recent patches has increased.
The flaw, CVE-2025-53770, pertains to the improper handling of untrusted data deserialization in SharePoint, allowing unauthorized users to execute arbitrary code remotely. This vulnerability impacts SharePoint Server versions 2016, 2019, and the Subscription Edition, while Microsoft 365 SharePoint Online remains secure from this threat.
Technical Breakdown of the Exploit
According to research from Viettel Cyber, attackers can exploit the vulnerability by manipulating XML schema processing within the ExcelDataSet control, which is a component of the PerformancePoint BI services. The targeted service is the BIMonitoringAuthoringService, specifically the TestConnection method used to validate data sources.
By injecting a DataSource object with a SourceName set to “ExcelWorkbook,” the exploit leverages an XmlSerializer to deserialize specific fields into an ExcelDataSet instance. This process bypasses the XmlValidator due to improper handling of XML schema imports, leading to execution of unauthorized types.
Vulnerability Exploitation Methodology
The PoC illustrates a method where an attacker manipulates the TestConnection endpoint to execute arbitrary code. This involves embedding a malicious XML payload that references an external XSD from a server controlled by the attacker. The external schema imports are not adequately checked by XmlValidator, allowing for execution of harmful code.
The exploit culminates in the execution of a command like launching win32calc.exe on the SharePoint server, demonstrating the vulnerability’s potential for severe impact. The attack can be carried out using a low-privileged account and involves hosting an external schema file accessible by the SharePoint server.
Mitigation and Security Recommendations
Security experts have observed active exploitation of CVE-2025-53770, emphasizing the urgency for organizations to apply the latest patches from Microsoft. To defend against such attacks, it is recommended to enable AMSI integration, rotate ASP.NET MachineKey values, and conduct thorough threat assessments focusing on PerformancePoint and ViewState activities.
In light of the detailed methodologies available, the potential for copycat attacks is heightened. Organizations utilizing on-premises SharePoint should prioritize these security measures to safeguard their systems against this critical vulnerability.
Stay informed and proactive to protect your infrastructure from emerging cyber threats.
