CVE-2023-21743 in SharePoint Server
Summary
by MITRE • 01/11/2023
Microsoft SharePoint Server Security Feature Bypass Vulnerability.
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Analysis
by VulDB Data Team • 09/22/2025
Microsoft SharePoint Server contains a security feature bypass vulnerability that allows attackers to circumvent access controls and potentially gain unauthorized access to sensitive information. This vulnerability affects multiple versions of SharePoint Server including 2016, 2019, and 2021, representing a significant risk to organizations relying on these platforms for document management and collaboration. The flaw stems from insufficient validation of user permissions within the SharePoint authorization framework, specifically in how the system handles certain API calls and authentication tokens. Attackers can exploit this weakness by crafting malicious requests that bypass the normal permission checking mechanisms, effectively allowing them to access documents, lists, and other SharePoint resources that they should not have access to based on their assigned roles. This vulnerability aligns with CWE-284 Access Control Issues, which encompasses problems related to inadequate access control mechanisms and permission enforcement. The security bypass occurs when SharePoint fails to properly validate whether a user has sufficient privileges to access specific resources, particularly in scenarios involving cross-site requests and API endpoint interactions. From an operational perspective, this vulnerability presents a critical risk as it can enable attackers to escalate privileges and access confidential business data, including proprietary documents, user information, and administrative resources. The impact extends beyond simple data theft to potential system compromise and lateral movement within the network. Organizations utilizing SharePoint Server may face regulatory compliance violations and significant financial losses due to unauthorized data access. The vulnerability also maps to ATT&CK technique T1078 Valid Accounts, as attackers can leverage this bypass to operate under seemingly legitimate user accounts while accessing restricted resources. The exploitation typically requires minimal privileges initially, making it particularly dangerous as attackers can use the vulnerability to gain broader access within the SharePoint environment.
The technical implementation of this security bypass involves the manipulation of SharePoint's internal permission checking logic during specific API interactions. When users make requests to SharePoint endpoints, the system should verify that the requesting user has appropriate permissions before granting access to requested resources. However, in vulnerable configurations, the permission validation process can be circumvented through carefully crafted requests that exploit gaps in the authorization framework. This weakness manifests particularly in how SharePoint handles token validation and session management, allowing attackers to reuse or manipulate authentication tokens to access resources beyond their intended scope. The vulnerability is further exacerbated by the fact that SharePoint Server's permission model is complex and hierarchical, making it difficult for administrators to fully understand and properly configure access controls. Attackers can exploit this by identifying specific API endpoints that do not perform adequate permission checks or by manipulating request parameters to bypass the normal authorization flow. The issue is compounded by SharePoint's integration with other Microsoft services, which can create additional attack vectors through cross-service authentication and authorization flows. Organizations should note that this vulnerability is particularly concerning because it can be exploited remotely without requiring direct system access, making detection and prevention more challenging.
Mitigation strategies for CVE-2023-21743 should include immediate deployment of Microsoft security patches and updates to address the underlying authorization bypass issue. Organizations must ensure that all SharePoint Server installations are updated to the latest security releases, as Microsoft has provided patches specifically designed to resolve this vulnerability. Network segmentation and monitoring should be implemented to detect unusual API access patterns that may indicate exploitation attempts. Access controls should be reviewed and strengthened, with particular attention to least privilege principles and role-based access control implementations. Regular security assessments and penetration testing should be conducted to identify potential exploitation vectors and validate the effectiveness of implemented controls. Additionally, organizations should implement robust logging and monitoring of SharePoint access activities, focusing on anomalous permission requests and cross-site resource access patterns. Security teams should also consider implementing additional authentication layers, such as multi-factor authentication, to reduce the impact of credential compromise. The vulnerability's classification as a security feature bypass underscores the importance of maintaining comprehensive security monitoring and incident response procedures. Organizations should also review their SharePoint Server configurations to ensure that default settings are not inadvertently creating additional attack surfaces. Regular vulnerability assessments should be conducted to identify similar weaknesses in other Microsoft products and services that may be integrated with SharePoint environments. The implementation of security awareness training for administrators and users can help prevent social engineering attacks that might be used to exploit this vulnerability. Given the potential for lateral movement within SharePoint environments, organizations should also consider implementing network access controls and endpoint protection measures to limit the damage that could result from successful exploitation.