CVE-2020-16871 in Dynamics 365
Summary
by MITRE
<p>A cross site scripting vulnerability exists when Microsoft Dynamics 365 (on-premises) does not properly sanitize a specially crafted web request to an affected Dynamics server. An authenticated attacker could exploit the vulnerability by sending a specially crafted request to an affected Dynamics 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 authenticated user. These attacks could allow the attacker to read content that the attacker is not authorized to read, use the victim's identity to take actions within Dynamics Server 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 Dynamics Server properly sanitizes web requests.</p>
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Analysis
by VulDB Data Team • 02/24/2026
This cross site scripting vulnerability in Microsoft Dynamics 365 on-premises represents a critical security flaw that allows authenticated attackers to execute malicious scripts within the context of legitimate user sessions. The vulnerability stems from insufficient input validation and sanitization mechanisms within the web request processing pipeline of the Dynamics server. According to CWE-79, this falls under the category of Cross-Site Scripting where the application fails to properly sanitize user-supplied data before incorporating it into dynamically generated web pages. The flaw specifically manifests when the server processes specially crafted web requests that contain malicious script payloads, which are then executed in the browser of authenticated users.
The operational impact of this vulnerability extends beyond simple script execution, creating a comprehensive attack surface that enables sophisticated malicious activities. An attacker who successfully exploits this vulnerability can leverage the authenticated user context to perform unauthorized actions within the Dynamics environment, including modifying user permissions, deleting critical content, and accessing restricted data that would normally be protected from their access level. This privilege escalation capability aligns with ATT&CK technique T1078 which describes legitimate credentials being used to gain access to systems and resources. The malicious script injection can also be used to steal session cookies, redirect users to phishing sites, or manipulate the user interface to deceive victims into performing unintended actions.
The vulnerability's exploitation requires an authenticated attacker, which means the attack vector typically involves either credential compromise through phishing, password spraying, or other initial access techniques. Once inside the system, the attacker can leverage the XSS flaw to maintain persistence and expand their access within the Dynamics environment. The security update addresses this by implementing proper input sanitization mechanisms that filter or escape potentially dangerous characters and script elements from incoming web requests before they are processed or rendered to users. This remediation follows standard security practices for preventing XSS attacks and aligns with Microsoft's security hardening recommendations for web applications. Organizations should also implement additional defensive measures such as content security policies, web application firewalls, and regular security assessments to protect against similar vulnerabilities in their Dynamics deployments.