CVE-2026-102864 in SharePoint Server
Summary
by MITRE • 10/13/2026
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 • 10/14/2026
The vulnerability described constitutes a classic instance of Cross-Site Scripting, specifically categorized under CWE-79: Improper Neutralization of Input During Web Page Generation. This flaw resides within the web application layer of Microsoft Office SharePoint Server, where the system fails to adequately sanitize or validate user-supplied input before incorporating it into dynamically generated HTML content. When a malicious actor submits crafted data containing executable script fragments, such as JavaScript code embedded in URLs, form fields, or HTTP headers, the server processes this input without applying sufficient filtering rules. Consequently, when other users access the affected page, their browsers interpret the injected scripts as legitimate content originating from the trusted SharePoint domain. This breakdown in input validation allows an attacker to execute arbitrary client-side scripts within the security context of the target website, bypassing standard browser protections like the Same-Origin Policy that typically isolate web applications from one another.
The operational impact of this vulnerability extends beyond simple script execution and directly facilitates network-based spoofing attacks as noted in the description. By injecting malicious JavaScript, an attacker can manipulate the Document Object Model to create fake login forms or deceptive UI elements that mimic legitimate SharePoint interfaces. This technique is often referred to as a phishing overlay or clickjacking variant, where users are tricked into entering credentials or sensitive data into fields controlled by the attacker’s script rather than the actual application. Furthermore, because the scripts run with the privileges of the authenticated user session, an authorized but malicious insider could potentially exfiltrate cookies, session tokens, and other authentication artifacts to hijack active sessions on behalf of legitimate users. This capability enables unauthorized access to restricted areas of the SharePoint environment, leading to potential data breaches, integrity violations, and a significant compromise of trust within the organizational network infrastructure.
From an offensive security perspective, this vulnerability aligns with several tactics in the MITRE ATT&CK framework. It primarily falls under the Execution tactic via Browser Rendering Engine techniques, where malicious code is executed on the victim's machine through their web browser. Additionally, it relates to Collection and Credential Access strategies, as the injected scripts can harvest sensitive information such as usernames, passwords, and multi-factor authentication tokens directly from the user’s active session. The ability to perform spoofing also connects to Defense Evasion techniques that involve masquerading or bypassing security controls by exploiting trust relationships between users and specific web domains. Understanding these mappings is crucial for defenders who need to monitor for indicators of compromise associated with client-side attacks, such as unusual outbound network traffic from browsers or anomalies in session management logs.
Mitigation strategies must address both the immediate technical flaw and broader architectural weaknesses. The most effective remediation involves implementing strict input validation and output encoding on all server-side pages that process user data. Developers should ensure that any dynamic content is encoded according to its context, such as HTML entity encoding for text nodes or URL encoding for query parameters, preventing the browser from interpreting malicious payloads as executable code. Additionally, deploying a Web Application Firewall can provide an additional layer of defense by filtering out known attack patterns before they reach the application server. On the administrative side, enforcing Content Security Policy headers is critical; this allows administrators to define which sources are permitted to execute scripts, thereby neutralizing the impact of any successfully injected payloads even if validation fails. Regular security audits and code reviews focused on input handling practices will further reduce the risk surface for such vulnerabilities in SharePoint environments.