CVE-2020-1173 in Power BI Report Server
Summary
by MITRE
A spoofing vulnerability exists in Microsoft Power BI Report Server in the way it validates the content-type of uploaded attachments, aka 'Microsoft Power BI Report Server Spoofing Vulnerability'.
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Analysis
by VulDB Data Team • 10/17/2020
The Microsoft Power BI Report Server spoofing vulnerability identified as CVE-2020-1173 represents a critical security flaw in the server's content validation mechanisms that enables attackers to manipulate file type detection and potentially execute malicious payloads. This vulnerability specifically targets the server's handling of uploaded attachments and demonstrates a fundamental weakness in the content-type validation process that is essential for maintaining the integrity of file uploads within enterprise reporting environments. The issue stems from insufficient validation of MIME content types during file upload operations, creating opportunities for attackers to bypass security controls that rely on proper file type identification.
The technical flaw manifests when the Power BI Report Server fails to properly validate the content-type header of uploaded files, allowing malicious actors to manipulate this parameter to disguise malicious files as benign types. This weakness enables attackers to upload files with deceptive content-type headers that may appear to be harmless documents or images while actually containing executable code or malicious payloads. The vulnerability operates at the application layer and specifically affects the server's file validation logic, where the system should enforce strict content-type checking but instead accepts manipulated headers without proper verification. According to CWE classification, this vulnerability maps to CWE-434 which describes "Unrestricted Upload of File with Dangerous Type" and represents a variant of insecure file upload vulnerabilities that have been consistently exploited in enterprise environments.
The operational impact of this vulnerability extends beyond simple file manipulation as it creates potential attack vectors for more sophisticated exploitation techniques within enterprise networks. Attackers can leverage this flaw to upload malicious files that may bypass security scanning mechanisms, as the server's content-type validation fails to properly identify the true nature of the uploaded files. This vulnerability particularly affects organizations that rely on Power BI Report Server for sensitive data reporting and analysis, as it could enable unauthorized access to reporting environments and potentially lead to data exfiltration or system compromise. The attack surface includes scenarios where users upload attachments to reports, and the server processes these files without adequate content-type verification, creating opportunities for attackers to establish persistence or escalate privileges within the reporting infrastructure.
Organizations utilizing Microsoft Power BI Report Server must implement comprehensive mitigation strategies to address this vulnerability effectively. The primary recommendation involves applying the official Microsoft security patches and updates that address the content-type validation flaw in the server's file handling mechanisms. Additionally, organizations should implement network-level restrictions that limit file upload capabilities to trusted sources and enforce strict content-type validation at multiple layers of the infrastructure. Security controls should include mandatory file type validation, content scanning of uploaded files, and implementation of proper access controls that limit user privileges for file upload operations. From an ATT&CK framework perspective, this vulnerability aligns with techniques such as T1133 - External Remote Services and T1078 - Valid Accounts, as it enables attackers to establish unauthorized access through manipulated file uploads and potentially escalate privileges within the reporting environment. The vulnerability also demonstrates characteristics of T1566 - Phishing, as attackers may use deceptive file types to trick users into uploading malicious content, making it critical for organizations to implement user education and awareness programs alongside technical controls.