CVE-2020-0891 in SharePoint Enterprise Server
Summary
by MITRE
This vulnerability is caused when SharePoint Server does not properly sanitize a specially crafted request to an affected SharePoint server.An authenticated attacker could exploit this vulnerability by sending a specially crafted request to an affected SharePoint server, aka 'Microsoft SharePoint Reflective XSS Vulnerability'. This CVE ID is unique from CVE-2020-0795.
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Analysis
by VulDB Data Team • 05/12/2025
The vulnerability identified as CVE-2020-0891 represents a critical cross-site scripting flaw within Microsoft SharePoint Server that arises from inadequate input sanitization mechanisms. This weakness specifically manifests when the affected SharePoint server receives a maliciously crafted request that exploits the system's failure to properly validate and sanitize user-supplied input. The vulnerability operates at the application layer and affects SharePoint Server implementations that do not adequately filter or escape potentially dangerous characters and sequences in incoming HTTP requests. The flaw enables an authenticated attacker to inject malicious scripts into web pages viewed by other users, creating a persistent security risk that can be exploited through legitimate user interactions with the vulnerable system.
The technical exploitation of CVE-2020-0891 leverages reflective cross-site scripting mechanisms where attacker-controlled input is reflected back to users without proper sanitization or encoding. This vulnerability falls under the CWE-79 category of Cross-Site Scripting, specifically classified as a reflective XSS variant where the malicious payload is reflected off the web server rather than being stored. The attack requires an authenticated user session to be effective, meaning that an attacker must first obtain valid credentials or exploit another vulnerability to gain access to a legitimate user account before executing the XSS payload. The vulnerability is particularly concerning because SharePoint servers often contain sensitive organizational data and may be accessed by users with elevated privileges, amplifying the potential impact of successful exploitation.
From an operational perspective, the exploitation of this vulnerability can lead to severe consequences including unauthorized data access, session hijacking, and potential lateral movement within the network. Attackers can craft malicious payloads that redirect users to phishing sites, steal session cookies, or execute malicious scripts that compromise user browsers and potentially escalate privileges. The reflective nature of the vulnerability means that the attack payload is delivered through a single request and executed immediately when the victim accesses the malicious link or page. This characteristic makes the vulnerability particularly dangerous in targeted attack scenarios where attackers can craft specific payloads to exploit individual users or groups within an organization. The vulnerability also impacts SharePoint's document management and collaboration features, potentially exposing sensitive business information and intellectual property to unauthorized access.
Mitigation strategies for CVE-2020-0891 should focus on implementing robust input validation and output encoding mechanisms within SharePoint Server configurations. Organizations should ensure that all user-supplied input is properly sanitized and that appropriate security headers are implemented to prevent XSS attacks. Microsoft recommends applying the latest security patches and updates to address this vulnerability, while also implementing additional protective measures such as content security policies and web application firewalls. The implementation of proper authentication controls and user access management can help limit the scope of potential exploitation, as the vulnerability requires authenticated access to function effectively. Security teams should also conduct regular vulnerability assessments and penetration testing to identify similar weaknesses in SharePoint configurations and ensure that input sanitization mechanisms are properly configured across all affected systems. Additionally, user education and awareness programs should be implemented to help identify and avoid potentially malicious links or content that may attempt to exploit this vulnerability through social engineering attacks.