CVE-2020-1591 in Dynamics 365
Summary
by MITRE
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. 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. The security update addresses the vulnerability by helping to ensure that Dynamics Server properly sanitizes web requests.
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Analysis
by VulDB Data Team • 02/24/2026
The vulnerability identified as CVE-2020-1591 represents a critical cross site scripting flaw within Microsoft Dynamics 365 on-premises deployments that stems from inadequate input validation mechanisms. This weakness specifically manifests when the system fails to properly sanitize web requests containing malicious payloads, creating an exploitable vector for authenticated attackers to manipulate the application's behavior. The vulnerability resides in the server-side request processing logic where user-supplied data is not adequately filtered or escaped before being rendered in web responses, allowing attackers to inject malicious scripts that execute within the context of legitimate user sessions.
The technical implementation of this vulnerability aligns with CWE-79 which specifically addresses cross site scripting weaknesses in web applications. Attackers exploiting this flaw can leverage the authenticated session to execute arbitrary scripts against the Dynamics 365 server, effectively operating under the privileges and permissions of the compromised user account. The attack surface is particularly concerning because it allows for privilege escalation and lateral movement within the system, as the malicious scripts can access and manipulate data that the user normally wouldn't have authorization to view or modify. This creates a direct pathway for data exfiltration, unauthorized access to sensitive business information, and potential system compromise through the execution of malicious code within the browser context of authenticated users.
The operational impact of CVE-2020-1591 extends beyond simple script execution, as it enables sophisticated attack patterns that can persistently compromise the Dynamics 365 environment. An attacker could use this vulnerability to establish a foothold within the organization's customer relationship management system, potentially accessing confidential customer data, modifying business processes, and altering system permissions to maintain persistent access. The attack could result in unauthorized content deletion, modification of business rules, and complete compromise of the integrity and confidentiality of the Dynamics 365 deployment. From an attack chain perspective, this vulnerability maps to multiple ATT&CK techniques including T1059 for command and scripting interpreter execution and T1566 for credential harvesting through social engineering.
Microsoft's security update for CVE-2020-1591 addresses the root cause by implementing proper input sanitization mechanisms that ensure all web requests are properly validated and filtered before processing. The fix enforces strict content validation rules that prevent malicious payloads from being executed within the application context, effectively neutralizing the XSS attack vector. Organizations should implement this patch immediately as the vulnerability requires only authenticated access to exploit, meaning that any compromised user account could potentially be leveraged by attackers. Additional mitigations include implementing web application firewalls, monitoring for suspicious request patterns, and conducting regular security assessments of the Dynamics 365 environment to identify potential exploitation attempts. The vulnerability demonstrates the critical importance of input validation in enterprise applications and serves as a reminder of the potential damage that can result from inadequate security controls in business-critical systems.