CVE-2026-55126 in SharePoint Server
Summary
by MITRE • 07/14/2026
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.
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Analysis
by VulDB Data Team • 07/15/2026
Cross-site scripting vulnerabilities in Microsoft Office SharePoint represent a critical security weakness that enables authenticated attackers to manipulate web page content through malicious input. This vulnerability falls under the CWE-79 category of Cross-Site Scripting, where insufficient input sanitization allows attackers to inject malicious scripts into web pages viewed by other users. The flaw specifically manifests during the web page generation process within SharePoint's rendering engine, creating an environment where user-supplied data can be improperly handled without adequate security controls.
The technical implementation of this vulnerability stems from SharePoint's failure to properly neutralize or escape user input before incorporating it into dynamically generated web content. When authorized users submit content through SharePoint interfaces such as discussion boards, document libraries, or web part configurations, the system does not adequately validate or sanitize the input parameters. This insufficient sanitization creates opportunities for attackers to inject malicious scripts that execute within the context of other users' browsers, particularly when those users view pages containing the compromised content.
The operational impact of this vulnerability extends beyond simple script execution to enable sophisticated social engineering attacks and session hijacking operations. An attacker with valid SharePoint credentials can craft malicious payloads that appear legitimate to end users, potentially leading to credential theft, privilege escalation, or data exfiltration. The spoofing capability allows attackers to manipulate the visual presentation of web pages, making it difficult for users to distinguish between authentic content and maliciously injected elements. This vulnerability particularly affects organizations relying heavily on SharePoint collaboration features, as it can be exploited through various attack vectors including user-generated content, web part configurations, and custom page templates.
Organizations should implement comprehensive mitigation strategies that align with industry best practices and security frameworks such as those outlined in the OWASP Top Ten and NIST cybersecurity guidelines. The primary defense mechanism involves implementing robust input validation and output encoding controls throughout the SharePoint application stack, ensuring all user-supplied content undergoes proper sanitization before being rendered to end users. Additionally, implementing strict access controls and monitoring user activities can help detect anomalous behavior indicative of exploitation attempts. Security patches from Microsoft should be applied promptly, as the company regularly releases updates addressing known XSS vulnerabilities in SharePoint environments.
The vulnerability demonstrates how seemingly minor input handling deficiencies can create significant security risks in enterprise collaboration platforms where users frequently interact with dynamic content. Organizations must consider implementing Content Security Policy headers, regular security assessments of SharePoint configurations, and user education programs to reduce the attack surface. This particular weakness highlights the importance of maintaining secure coding practices and comprehensive testing procedures for web applications, particularly those handling user-generated content. The exploitation of such vulnerabilities can result in widespread compromise across organizational networks, emphasizing the need for proactive security measures and continuous monitoring of SharePoint environments against evolving threats.