CVE-2026-64902 in SharePoint Server
Summary
by MITRE • 08/11/2026
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.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 08/16/2026
The vulnerability described constitutes a classic Cross-Site Scripting (XSS) flaw within the Microsoft Office SharePoint environment, specifically categorized under CWE-79: Improper Neutralization of Input During Web Page Generation. This security weakness arises from insufficient validation or sanitization of user-supplied input before it is rendered in an HTML context by the web server. In this specific instance, the failure to properly neutralize special characters allows malicious scripts to be injected into web pages that are subsequently viewed by other users. While the prompt notes that an authorized attacker can exploit this, it is critical to clarify that XSS vulnerabilities typically allow attackers who have valid credentials or access to input fields on a SharePoint site to execute arbitrary client-side script in the browsers of other authenticated users. The term spoofing mentioned likely refers to session hijacking or credential theft rather than network-level IP spoofing, as XSS operates at the application layer by manipulating the victim's browser context.
From an operational perspective, this vulnerability poses significant risks to data integrity and confidentiality within enterprise environments relying on SharePoint for collaboration and document management. An attacker leveraging this flaw can execute malicious JavaScript in the context of the trusted domain hosting SharePoint. This enables several severe attack vectors including stealing session cookies or authentication tokens, which allows the attacker to impersonate legitimate users without needing their passwords. Furthermore, it facilitates keylogging capabilities where keystrokes entered into forms on the site are captured and sent to a remote server controlled by the attacker. It can also be used to deface web pages or redirect users to malicious sites designed for phishing attacks, thereby undermining trust in the organization's internal communication channels.
The technical mechanism involves the application taking user input such as comments, profile information, or document metadata without adequately encoding characters like angle brackets, quotes, and ampersands that have special meaning in HTML and JavaScript. When this untrusted data is embedded into a dynamic web page response, the browser interprets it not as plain text but as executable code. This bypasses same-origin policy protections because the script runs with the privileges of the SharePoint domain itself. Attackers often craft payloads using event handlers or DOM manipulation techniques to trigger execution upon specific user interactions such as hovering over an element or submitting a form. The persistence of this vulnerability depends on whether the input is stored in a database and served later (Stored XSS) or reflected immediately back to the browser (Reflected XSS), with Stored variants being particularly dangerous due their wider potential impact across multiple users.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Immediately, Microsoft should apply available security patches that update the SharePoint software to versions where input validation logic has been hardened. For administrators unable to patch immediately, implementing strict Content Security Policy (CSP) headers can significantly reduce the impact by restricting the sources from which scripts are allowed to load and execute. Additionally, deploying Web Application Firewalls with robust XSS detection rules can help block malicious payloads before they reach the application server. From a development standpoint, developers must enforce output encoding based on the context in which data is rendered, ensuring that all special characters are converted into their corresponding HTML entities. Input validation should also be implemented to reject or sanitize unexpected character sequences at the point of entry.
This vulnerability aligns with MITRE ATT&CK technique T1059: Command and Scripting Interpreter, specifically under sub-techniques involving JavaScript execution in a browser context. It also relates to T1078: Valid Accounts if the attacker uses legitimate credentials to gain access to input fields. Addressing this issue requires a defense-in-depth approach combining secure coding practices, regular vulnerability assessments, and continuous monitoring for anomalous script executions within the SharePoint environment. Organizations should prioritize patch management cycles to ensure that known flaws in widely deployed enterprise software are addressed promptly to prevent exploitation by threat actors targeting internal networks.