CVE-2021-26420 in SharePoint Server
Summary
by MITRE • 06/09/2021
Microsoft SharePoint Server Remote Code Execution Vulnerability This CVE ID is unique from CVE-2021-31963, CVE-2021-31966.
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Analysis
by VulDB Data Team • 06/10/2021
Microsoft SharePoint Server contains a remote code execution vulnerability that arises from improper validation of user input within the web application's processing pipeline. This flaw exists in the way SharePoint handles certain HTTP requests and parameter values, allowing attackers to inject malicious code that executes with the privileges of the SharePoint service account. The vulnerability specifically impacts SharePoint Server 2019 and SharePoint Server 2016 versions, where the application fails to properly sanitize input parameters before processing them through internal rendering mechanisms. According to CWE-20, this represents a classic input validation flaw that enables attackers to manipulate application behavior through crafted malicious payloads. The vulnerability is particularly dangerous because it can be exploited without authentication, making it a significant threat to organizations that have not applied the relevant security patches. The attack vector typically involves sending specially crafted HTTP requests that contain malicious code within parameters that SharePoint processes during rendering operations. When the server processes these requests, the malformed input triggers code execution on the target system, potentially allowing attackers to gain full control over the SharePoint server infrastructure. This vulnerability aligns with ATT&CK technique T1190, which describes exploiting vulnerabilities in remote services to establish persistent access to target systems. The impact extends beyond simple code execution as it can lead to complete system compromise, data exfiltration, and lateral movement within the network. Organizations running affected SharePoint Server versions face significant risk of unauthorized access and potential data breaches. The flaw demonstrates how insufficient input validation can create pathways for attackers to escalate privileges and execute arbitrary commands on the server. Security researchers have identified that the vulnerability can be leveraged to deploy backdoors, modify web content, and access sensitive information stored within SharePoint repositories. The exploitation requires minimal user interaction and can be automated through various attack frameworks. Microsoft has released security updates addressing this vulnerability through the regular patching cycle, but organizations must ensure timely deployment of these patches to maintain system integrity. The vulnerability also highlights the importance of network segmentation and implementing proper access controls to limit potential damage from successful exploitation attempts. Organizations should consider implementing additional monitoring mechanisms to detect anomalous behavior patterns that might indicate exploitation attempts. The flaw underscores the critical need for regular security assessments and vulnerability management programs to identify and remediate similar issues before they can be exploited by threat actors. This vulnerability serves as a reminder of the ongoing challenges in securing complex enterprise applications and the necessity of maintaining up-to-date security practices across all system components. The technical implementation of SharePoint's input handling mechanisms requires careful review to prevent similar issues from occurring in future versions of the platform. Security teams must prioritize patch management processes to ensure that all SharePoint installations receive timely security updates and that appropriate testing procedures are in place before deployment. The exploitation of this vulnerability can result in severe business disruption and regulatory compliance violations, making proactive remediation essential for maintaining organizational security posture.