CVE-2021-1641 in SharePoint Server
Summary
by MITRE • 01/13/2021
Microsoft SharePoint Spoofing Vulnerability This CVE ID is unique from CVE-2021-1717.
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Analysis
by VulDB Data Team • 05/04/2025
The Microsoft SharePoint Spoofing Vulnerability identified as CVE-2021-1641 represents a significant security flaw in the SharePoint Server platform that allows attackers to manipulate user interfaces and potentially deceive end users. This vulnerability specifically affects Microsoft SharePoint Server 2016 and SharePoint Server 2019 installations, creating opportunities for malicious actors to exploit user trust mechanisms within the web-based collaboration platform. The flaw stems from insufficient validation of user-supplied input in SharePoint's rendering processes, enabling attackers to craft deceptive content that appears legitimate to users interacting with the system.
This vulnerability operates through a cross-site scripting attack vector where malicious actors can inject crafted HTML or JavaScript code into SharePoint pages, particularly affecting the user interface elements and navigation components. The technical implementation involves the improper handling of user input in SharePoint's server-side rendering functions, which fail to adequately sanitize or validate data before displaying it to authenticated users. When users browse SharePoint sites containing malicious content, the system renders the spoofed elements without proper security checks, allowing attackers to manipulate the visual presentation of web pages to mislead users about the true nature of the content they are interacting with.
The operational impact of CVE-2021-1641 extends beyond simple visual deception as it can facilitate more sophisticated attacks such as credential harvesting, session hijacking, or redirection to malicious websites. Attackers can leverage this vulnerability to create convincing phishing pages that mimic legitimate SharePoint interfaces, potentially capturing user credentials or sensitive information. The vulnerability's exploitation requires minimal privileges since it targets the user interface rendering rather than system-level access, making it particularly dangerous in enterprise environments where SharePoint serves as a primary collaboration platform. Security researchers have noted that this flaw aligns with CWE-79 which describes cross-site scripting vulnerabilities, and it can be mapped to ATT&CK technique T1566 for credential harvesting through social engineering.
Organizations affected by this vulnerability should prioritize immediate remediation through Microsoft's security updates and patches released in their January 2021 security bulletin. The recommended mitigation strategy involves applying the latest cumulative updates for SharePoint Server 2016 and SharePoint Server 2019, which address the input validation deficiencies in the affected rendering components. Network administrators should also implement additional security controls such as web application firewalls and content security policies to detect and prevent exploitation attempts. Regular security monitoring and user awareness training become critical components of defense in depth strategies, as the vulnerability's impact relies heavily on user interaction with maliciously crafted content. The vulnerability's classification as a medium severity issue by Microsoft underscores the importance of timely patch management while recognizing that exploitation typically requires user engagement with malicious content.