CVE-2021-1717 in SharePoint Server
Summary
by MITRE • 01/13/2021
Microsoft SharePoint Spoofing Vulnerability This CVE ID is unique from CVE-2021-1641.
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Analysis
by VulDB Data Team • 05/04/2025
The CVE-2021-1717 vulnerability represents a critical spoofing flaw in Microsoft SharePoint Server that enables attackers to manipulate user interfaces and potentially deceive users into performing unintended actions. This vulnerability specifically affects SharePoint Server 2016 and SharePoint Server 2019 installations, making it a significant concern for organizations relying on these platforms for document management and collaboration services. The flaw resides in how SharePoint handles certain user interface elements and validation mechanisms, creating opportunities for malicious actors to craft deceptive experiences that appear legitimate to end users.
This vulnerability stems from inadequate input validation and insufficient sanitization of user-provided content within SharePoint's rendering pipeline. Attackers can exploit this weakness by crafting malicious payloads that manipulate the display of web pages, potentially causing users to believe they are interacting with legitimate SharePoint interfaces while actually engaging with attacker-controlled content. The technical implementation involves manipulating the way SharePoint processes and displays certain HTML elements, particularly those related to navigation controls and user interface components. This allows adversaries to create misleading visual presentations that could trick users into revealing credentials, clicking on malicious links, or performing other harmful actions.
The operational impact of CVE-2021-1717 extends beyond simple deception, as it can serve as a precursor to more serious attacks within enterprise environments. When exploited successfully, this vulnerability enables attackers to conduct phishing campaigns that are more convincing than traditional methods, as they leverage the legitimate SharePoint interface to mask malicious activities. Organizations may experience unauthorized access attempts, credential harvesting, and potential data exfiltration through this vector. The vulnerability's exploitation typically requires minimal privileges and can be executed through web-based attacks, making it particularly dangerous for environments where SharePoint serves as a primary collaboration platform. Security professionals have noted that this vulnerability can be combined with other attack vectors to create more sophisticated multi-stage attacks.
Mitigation strategies for CVE-2021-1717 focus on both immediate patching and operational security improvements. Microsoft has released security updates that address the underlying validation issues in SharePoint Server 2016 and 2019, and organizations should prioritize applying these patches to eliminate the vulnerability. Network segmentation and monitoring of SharePoint traffic can help detect anomalous behavior that might indicate exploitation attempts. Additionally, implementing strict content filtering and user access controls can reduce the potential impact of successful attacks. The vulnerability aligns with CWE-79 which addresses cross-site scripting flaws, and can be categorized under ATT&CK technique T1566 for social engineering attacks. Organizations should also consider implementing security awareness training to help users recognize deceptive interfaces and maintain vigilance against potentially malicious SharePoint interactions. Regular security assessments and penetration testing of SharePoint environments can help identify additional weaknesses that might be exploited in conjunction with this vulnerability.