CVE-2021-24104 in Word
Summary
by MITRE • 03/11/2021
Microsoft SharePoint Spoofing Vulnerability
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Analysis
by VulDB Data Team • 03/30/2021
The CVE-2021-24104 vulnerability represents a cross-site scripting flaw in Microsoft SharePoint Server that allows attackers to perform spoofing attacks by injecting malicious scripts into web pages viewed by users. This vulnerability specifically affects SharePoint Server 2019 and SharePoint Server 2016 versions, creating a significant security risk for organizations relying on these platforms for document management and collaboration services. The flaw resides in how SharePoint handles certain input validation mechanisms within its web interface, particularly when processing user-provided content that gets rendered in web contexts without proper sanitization.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding within SharePoint's rendering engine. When users submit content or interact with SharePoint features that involve dynamic content generation, the system fails to adequately sanitize user inputs before displaying them in web contexts. This allows attackers to craft malicious payloads that can execute within the victim's browser context, potentially leading to session hijacking, credential theft, or unauthorized access to sensitive information. The vulnerability operates under CWE-79 which specifically addresses Cross-Site Scripting (XSS) flaws, where applications fail to properly validate or encode user-supplied data before incorporating it into dynamically generated web content.
The operational impact of this vulnerability extends beyond simple script execution as it enables sophisticated attack vectors that can compromise entire SharePoint environments. Attackers can leverage this flaw to manipulate the SharePoint user interface, redirect users to malicious sites, or inject persistent scripts that maintain control over user sessions. The spoofing capability allows threat actors to create convincing fake login pages or manipulate content presentation to deceive users into divulging sensitive information. Organizations may experience unauthorized access to confidential documents, data breaches, and potential lateral movement within their network infrastructure, as SharePoint often serves as a central hub for internal collaboration and file sharing.
Mitigation strategies for CVE-2021-24104 should include immediate application of Microsoft security patches and updates released through the Microsoft Security Response Center. Organizations must implement comprehensive input validation mechanisms and ensure proper output encoding across all SharePoint web applications to prevent script injection attacks. Network segmentation and web application firewalls can provide additional layers of protection by monitoring and filtering suspicious traffic patterns. Security teams should conduct regular vulnerability assessments and penetration testing to identify potential exploitation vectors, while implementing user education programs to recognize social engineering attempts that may accompany such attacks. The ATT&CK framework categorizes this vulnerability under T1531 which involves Account Access Removal, and T1059 which covers Command and Scripting Interpreter, highlighting the potential for attackers to escalate privileges and maintain persistent access through the compromised SharePoint environment.