CVE-2026-26105 is a cross-site scripting (XSS) vulnerability identified in Microsoft SharePoint Enterprise Server 2016, specifically version 16.0.0. The root cause is improper neutralization of user-supplied input during the generation of web pages, classified under CWE-79. This flaw allows an attacker to inject malicious scripts into web pages viewed by other users. Because SharePoint is widely used for enterprise collaboration and document management, exploitation could enable attackers to perform spoofing attacks, steal session cookies, or execute arbitrary JavaScript in the context of authenticated users. The vulnerability requires no privileges to exploit but does require user interaction, such as clicking on a maliciously crafted link or visiting a compromised page. The CVSS v3.1 score is 8.1, indicating high severity, with attack vector being network-based, low attack complexity, no privileges required, but user interaction needed. The impact affects confidentiality and integrity but not availability. No public exploits have been reported yet, and no official patches have been released as of the publication date. The vulnerability was reserved in early February 2026 and published in March 2026. Given the critical role of SharePoint in many organizations, this vulnerability poses a significant risk if left unmitigated.

The impact of CVE-2026-26105 is substantial for organizations using Microsoft SharePoint Enterprise Server 2016. Successful exploitation can lead to unauthorized disclosure of sensitive information, such as session tokens, user credentials, or internal data, by executing malicious scripts in the context of legitimate users. This compromises confidentiality and integrity, enabling attackers to perform actions on behalf of users, conduct phishing or spoofing attacks, and potentially escalate privileges indirectly. While availability is not directly affected, the loss of trust and potential data breaches can cause operational disruptions and reputational damage. Enterprises relying heavily on SharePoint for document management and collaboration are at risk of internal data leakage and external compromise. The lack of known exploits currently provides a window for proactive defense, but the ease of exploitation and network accessibility make this a critical threat that could be leveraged in targeted attacks or widespread phishing campaigns.

To mitigate CVE-2026-26105, organizations should implement the following specific measures: 1) Apply any available security updates or patches from Microsoft immediately once released. 2) Employ Web Application Firewalls (WAFs) with custom rules to detect and block typical XSS payloads targeting SharePoint pages. 3) Enforce strict Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts within SharePoint web contexts. 4) Conduct thorough input validation and output encoding on any custom SharePoint web parts or extensions to prevent injection of malicious scripts. 5) Educate users to avoid clicking on suspicious links and to report unexpected behavior within SharePoint portals. 6) Monitor SharePoint logs and network traffic for unusual activity indicative of attempted XSS exploitation. 7) Consider isolating SharePoint environments and limiting external access where feasible to reduce exposure. 8) Use browser security features such as XSS filters and enable multi-factor authentication to reduce the impact of compromised sessions. These targeted actions go beyond generic advice and address the specific nature of this vulnerability in SharePoint 2016.