CVE-2021-34519 in SharePoint Server
Summary
by MITRE • 07/15/2021
Microsoft SharePoint Server Information Disclosure Vulnerability
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Analysis
by VulDB Data Team • 07/17/2021
Microsoft SharePoint Server contains an information disclosure vulnerability that arises from improper validation of user input within the web application's authentication and authorization mechanisms. This flaw exists in the way SharePoint processes certain HTTP requests and handles authentication tokens, allowing unauthorized users to potentially access sensitive information that should be restricted to authenticated administrators or specific user groups. The vulnerability specifically impacts SharePoint Server 2016 and SharePoint Server 2019 installations where the affected components fail to properly sanitize input parameters before processing them in authentication contexts. Attackers can exploit this weakness by crafting malicious requests that bypass normal access controls and retrieve information that would otherwise be protected by the system's security model.
The technical implementation of this vulnerability stems from a lack of proper input sanitization and validation within SharePoint's authentication pipeline. When processing certain HTTP headers or query parameters, the system does not adequately verify the legitimacy of the provided data before attempting to authenticate or authorize the request. This creates a scenario where malformed or specially crafted input can cause the system to disclose internal information about user accounts, system configurations, or administrative privileges. The flaw operates at the application layer and can be exploited through standard web-based attack vectors without requiring elevated privileges or specialized tools. According to CWE-200, this vulnerability maps to improper information exposure, while the ATT&CK framework categorizes this under T1212 - Exploitation for Credential Access, as the disclosure can potentially lead to credential compromise or privilege escalation.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can provide attackers with critical insights into the internal structure and configuration of SharePoint environments. An attacker who successfully exploits this vulnerability could gain knowledge about user account structures, administrative access patterns, and system security configurations that would significantly aid in planning more sophisticated attacks. The disclosure may include details about user permissions, group memberships, or authentication mechanisms that could be leveraged to escalate privileges or conduct further reconnaissance. Organizations running affected SharePoint Server versions face potential exposure to insider threats or external attacks that could result in unauthorized access to sensitive corporate data, document repositories, or administrative controls. The vulnerability particularly affects environments where SharePoint serves as a central collaboration platform with extensive user access controls and sensitive information storage.
Mitigation strategies for this vulnerability require immediate implementation of Microsoft security patches and updates to affected SharePoint Server installations. Organizations should prioritize applying the relevant security updates from Microsoft's official security bulletin, which address the specific input validation issues within the authentication components. Network administrators should also implement additional monitoring and logging controls to detect anomalous authentication requests or unusual access patterns that might indicate exploitation attempts. Access control configurations should be reviewed to ensure that least privilege principles are maintained and that unnecessary administrative access is minimized. Security teams should consider implementing web application firewalls or intrusion detection systems that can identify and block suspicious request patterns targeting this specific vulnerability. Regular security assessments and vulnerability scanning should be conducted to identify any other potential weaknesses in the SharePoint environment that could be exploited in conjunction with this information disclosure flaw.