CVE-2026-55020 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 • 07/14/2026
Cross-site scripting vulnerabilities in Microsoft Office SharePoint represent a critical security flaw that enables authenticated attackers to execute malicious scripts within the context of other users' browsers. This particular vulnerability stems from inadequate input validation and sanitization during web page generation processes, creating an environment where malicious code can be injected and subsequently executed without proper neutralization measures. The flaw resides in SharePoint's handling of user-supplied data within web content rendering pipelines, allowing attackers who have valid credentials to manipulate the application's output generation mechanisms.
The technical exploitation of this vulnerability occurs when an attacker with authorized access submits malicious input through SharePoint's web interface or API endpoints that are designed to accept user-generated content. The system fails to properly sanitize or escape special characters in the input data before incorporating it into dynamically generated HTML pages, enabling script execution when other users view the compromised content. This creates a persistent threat vector where attackers can leverage their legitimate access privileges to inject malicious payloads that execute in the victim's browser context, potentially leading to session hijacking, data theft, or further privilege escalation.
The operational impact of this vulnerability extends beyond simple script injection, as it enables sophisticated attack patterns including session manipulation, credential harvesting, and unauthorized data access. Attackers can craft malicious content that appears legitimate to end users while simultaneously executing harmful scripts that compromise user sessions or redirect traffic to malicious sites. This vulnerability particularly affects organizations relying on SharePoint for collaborative environments where users frequently create and share web content, as the attack surface expands with increased user interaction and content generation activities.
Security professionals should implement multiple layers of defense including input validation at all entry points, proper output encoding for web content, and regular security updates from Microsoft to address known vulnerabilities. Organizations must enforce strict access controls and monitor user activities for suspicious content creation patterns. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws in web applications, and maps to ATT&CK technique T1566 related to spearphishing attacks that leverage web-based exploitation methods. Mitigation strategies include deploying web application firewalls, implementing content security policies, and conducting regular security assessments of SharePoint environments to identify potential injection points and validate proper input sanitization measures.