CVE-2026-55135 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 execute malicious scripts within the context of other users' browsers. This particular vulnerability stems from insufficient input validation during web page generation processes, creating an attack surface where malicious data can be injected into web content without proper sanitization. The flaw specifically manifests when SharePoint fails to adequately neutralize user-supplied input before rendering it in web pages, allowing attackers to embed malicious scripts that execute in the victim's browser context.
The technical implementation of this vulnerability involves the manipulation of SharePoint's content handling mechanisms where user-provided data enters the system through various entry points including document libraries, discussion boards, or custom web parts. When the system processes this input for display in web pages, the absence of proper encoding or filtering allows malicious payloads to persist and execute when other users view the affected content. This creates a persistent threat vector where attackers can craft specially crafted input that appears legitimate but contains embedded script code designed to steal session cookies, redirect users to malicious sites, or perform unauthorized actions within the SharePoint environment.
The operational impact of this vulnerability extends beyond simple data theft or redirection attacks, as it enables sophisticated social engineering campaigns and privilege escalation attempts. An authenticated attacker with access to SharePoint can leverage this weakness to create convincing phishing attacks that appear legitimate within the organization's trusted environment, potentially bypassing traditional security controls. The attack can be particularly damaging in enterprise settings where SharePoint serves as a central collaboration platform, as successful exploitation could lead to unauthorized access to sensitive corporate data, disruption of business operations, and potential lateral movement within the network infrastructure.
Mitigation strategies for this vulnerability should encompass multiple defensive layers including input validation at all entry points, proper output encoding of user-supplied content, regular security updates from Microsoft, and implementation of web application firewalls. Organizations should also consider deploying content security policies to restrict script execution in SharePoint environments and establish strict access controls to limit the impact of compromised accounts. 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 application vulnerabilities. Regular security assessments and penetration testing should be conducted to identify similar weaknesses in SharePoint configurations and ensure that all input handling processes properly sanitize data before rendering it in web contexts.