CVE-2026-55040 in SharePoint Server
Summary
by MITRE • 07/14/2026
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
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Analysis
by VulDB Data Team • 07/14/2026
This vulnerability represents a critical weakness in Microsoft Office SharePoint's authentication mechanism that enables unauthorized access through network-based attacks. The flaw stems from insufficient validation of credentials or improper implementation of authentication protocols, allowing attackers to circumvent security controls that should otherwise restrict access to SharePoint resources. Such weaknesses typically arise from inadequate session management, weak credential handling, or flawed authorization checks within the SharePoint infrastructure. The vulnerability can be exploited remotely without requiring physical access to the system, making it particularly dangerous in networked environments where SharePoint servers are accessible to external parties. Attackers may leverage this weakness to gain unauthorized access to sensitive documents, modify content, execute malicious code, or escalate privileges within the SharePoint environment.
The technical implementation of this authentication bypass typically involves exploiting design flaws in how SharePoint validates user credentials or manages authenticated sessions. Common vectors include weak password policies, predictable session identifiers, improper error handling that reveals authentication state, or vulnerabilities in the authentication pipeline itself. This weakness can be classified under CWE-287 which addresses improper authentication issues and aligns with ATT&CK technique T1078 for valid accounts and T1566 for credential stuffing attacks. The vulnerability may manifest through various attack patterns including session hijacking, brute force attempts, or exploitation of misconfigured authentication modules within SharePoint's architecture.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass significant data breach risks and potential system compromise. Organizations utilizing SharePoint may face exposure of confidential business information, intellectual property theft, regulatory compliance violations, and reputational damage when such authentication flaws remain unaddressed. The attack surface expands considerably as SharePoint servers often contain sensitive organizational data including proprietary documents, employee records, and strategic business information. Additionally, successful exploitation can serve as a foothold for lateral movement within networks, potentially enabling attackers to access other systems connected to the same infrastructure.
Mitigation strategies should focus on implementing robust authentication controls including multi-factor authentication deployment, regular security patching of SharePoint components, proper configuration of authentication modules, and network segmentation to limit exposure. Organizations must conduct thorough vulnerability assessments to identify misconfigurations in their SharePoint environments and implement monitoring solutions to detect suspicious authentication attempts. Security controls should include enforcing strong password policies, implementing account lockout mechanisms, regularly reviewing access permissions, and establishing secure remote access protocols. The implementation of security standards such as NIST SP 800-53 and ISO 27001 frameworks can help organizations establish comprehensive authentication security measures that address the root causes of these vulnerabilities while maintaining operational efficiency.