CVE-2020-1345 in SharePoint Server
Summary
by MITRE
<p>A cross-site-scripting (XSS) vulnerability exists when Microsoft SharePoint Server does not properly sanitize a specially crafted web request to an affected SharePoint server. An authenticated attacker could exploit the vulnerability by sending a specially crafted request to an affected SharePoint server.</p> <p>The attacker who successfully exploited the vulnerability could then perform cross-site scripting attacks on affected systems and run script in the security context of the current user. The attacks could allow the attacker to read content that the attacker is not authorized to read, use the victim's identity to take actions on the SharePoint site on behalf of the user, such as change permissions and delete content, and inject malicious content in the browser of the user.</p> <p>The security update addresses the vulnerability by helping to ensure that SharePoint Server properly sanitizes web requests.</p>
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Analysis
by VulDB Data Team • 02/24/2026
The vulnerability identified as CVE-2020-1345 represents a critical cross-site scripting flaw within Microsoft SharePoint Server that stems from inadequate input validation mechanisms. This vulnerability falls under the CWE-79 category, which specifically addresses cross-site scripting vulnerabilities where web applications fail to properly sanitize user-supplied data before incorporating it into web pages served to other users. The flaw exists in the server-side request handling process where SharePoint Server does not adequately sanitize web requests containing malicious script payloads, creating an attack surface that can be exploited by authenticated users.
Attackers exploiting this vulnerability can leverage the XSS flaw to execute arbitrary scripts within the context of authenticated users' browsers, effectively bypassing normal security boundaries. The exploitation process involves sending specially crafted web requests to the affected SharePoint server, which then processes these requests without proper sanitization, allowing malicious code to be injected into the server's response. This capability enables attackers to perform a wide range of malicious activities including session hijacking, privilege escalation, and data exfiltration. The vulnerability particularly impacts the authentication and authorization mechanisms of SharePoint environments, as successful exploitation allows attackers to impersonate legitimate users and perform actions within the SharePoint site that the user normally wouldn't be authorized to execute.
The operational impact of this vulnerability extends beyond simple script execution, as it fundamentally compromises the security model of SharePoint environments. Attackers can leverage the XSS vulnerability to read content that they should not have access to, modify permissions, delete critical content, and inject malicious scripts that persist across user sessions. This type of attack aligns with ATT&CK technique T1059.007 for command and control through scripting, and T1566 for credential access through spearphishing. The vulnerability also enables more sophisticated attacks such as token theft and session manipulation, where attackers can capture and reuse user authentication tokens to maintain persistent access to SharePoint systems. The security implications are particularly severe in enterprise environments where SharePoint servers often host sensitive business data and serve as central collaboration platforms.
Microsoft's security update for CVE-2020-1345 addresses the root cause by implementing enhanced input sanitization mechanisms within SharePoint Server's web request processing pipeline. The fix ensures that all user-supplied input is properly validated and sanitized before being incorporated into web responses, effectively neutralizing the XSS attack vector. Organizations should prioritize immediate deployment of this security update as part of their vulnerability management processes, particularly in environments where SharePoint servers handle sensitive data or serve as critical collaboration platforms. The mitigation strategy should also include network segmentation, monitoring for suspicious web requests, and regular security assessments of SharePoint environments to identify potential variants of this vulnerability or similar input validation flaws that may exist in other components of the SharePoint ecosystem.