CVE-2026-88204 in SharePoint Server
Summary
by MITRE • 10/14/2026
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 • 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 injects executable script code through these unsanitized inputs, the browser interprets and executes this code as if it originated from the trusted server domain. This breakdown in input validation represents a fundamental failure in implementing proper output encoding strategies, allowing client-side scripts to run within the security context of the SharePoint application rather than being treated as inert data.
The operational impact of this vulnerability extends beyond simple script execution, encompassing significant risks related to authentication spoofing and session hijacking. Because the injected scripts execute with the privileges of the authenticated user interacting with the vulnerable page, an attacker can manipulate the Document Object Model to mimic legitimate login interfaces or administrative panels. This capability facilitates network-based spoofing attacks where victims are tricked into entering credentials or sensitive data into fake forms controlled by the attacker. Furthermore, the malicious script can access session cookies and local storage tokens, enabling the adversary to hijack active user sessions without needing valid passwords. This effectively bypasses traditional authentication mechanisms and allows unauthorized access to restricted areas of the SharePoint environment.
From a threat intelligence perspective, this vulnerability aligns with several techniques defined in the MITRE ATT&CK framework. The initial exploitation phase corresponds to T1059: Command and Scripting Interpreter, as arbitrary scripts are executed within the victim's browser context. The subsequent goal of stealing credentials or session tokens maps directly to T1539: Steal Web Session Cookie, while the act of presenting a fake login page for credential harvesting is characteristic of T1621: Multi-Factor Authentication Interception and general phishing-based social engineering tactics often grouped under T1078: Valid Accounts. The attacker leverages these techniques to establish persistence or escalate privileges within the SharePoint infrastructure by impersonating legitimate users who have higher access rights than the initial compromised account.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Microsoft has released specific security updates that patch this vulnerability; organizations should prioritize applying the latest cumulative updates for their version of Office SharePoint Server to close the code-level defect. In addition to software patches, defensive measures include implementing a strict Content Security Policy (CSP) header which restricts the sources from which scripts can be loaded and executed, thereby neutralizing many cross-site scripting attacks even if input validation fails. Deploying Web Application Firewalls configured with robust XSS detection rules can also provide an additional layer of defense by filtering malicious payloads before they reach the application server. Finally, rigorous developer training on secure coding practices, particularly regarding output encoding and context-aware data sanitization, is essential to prevent similar vulnerabilities in custom web parts or third-party solutions integrated into the SharePoint environment.