CVE-2026-45464 Overview
CVE-2026-45464 is a cross-site scripting (XSS) vulnerability in Microsoft Office SharePoint Server. The flaw stems from improper neutralization of user-supplied input during web page generation [CWE-79]. An authenticated attacker can inject malicious script content that executes in the context of another user's browser session, enabling spoofing attacks over the network.
The vulnerability affects SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Server 2016 Enterprise. Exploitation requires low privileges and user interaction, and the scope changes when injected content executes in another security context.
Critical Impact
Authenticated attackers can inject scripts that execute in victim browsers, enabling content spoofing, session manipulation, and limited disclosure of confidential information from SharePoint sites.
Affected Products
- Microsoft SharePoint Server Subscription Edition
- Microsoft SharePoint Server 2019
- Microsoft SharePoint Server 2016 Enterprise
Discovery Timeline
- 2026-06-09 - CVE-2026-45464 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-45464
Vulnerability Analysis
The vulnerability resides in SharePoint Server's web page generation logic, where user-supplied input is not properly neutralized before being rendered in the response. When an attacker submits crafted content containing HTML or JavaScript markup, SharePoint reflects or stores that content without adequate output encoding.
The issue maps to [CWE-79], the canonical classification for cross-site scripting. SharePoint's rich content surfaces — list items, web parts, document properties, and discussion fields — provide multiple injection points where attacker-controlled markup can reach the rendered DOM.
The scope change indicates that injected script crosses a trust boundary at execution. Code provided by a low-privileged user runs in the browser context of higher-privileged users who view the affected page, including site administrators.
Root Cause
The root cause is missing or insufficient output encoding when SharePoint serializes user input into HTML responses. Input fields that accept text, URLs, or formatted content fail to escape characters such as <, >, ", and ' before insertion into the response body. As a result, browsers interpret attacker payloads as executable markup rather than literal text.
Attack Vector
Exploitation requires the attacker to hold valid SharePoint credentials with permission to create or modify content on a target site. The attacker submits a payload containing JavaScript through a vulnerable input surface, such as a list item title, document metadata field, or web part property. When another authenticated user navigates to the affected page, the browser parses and executes the injected script under the SharePoint site's origin.
Because the script runs in the victim's session context, the attacker can perform actions on behalf of the victim, alter rendered content to impersonate trusted UI elements, or harvest information visible to the victim. The Microsoft advisory categorizes the primary impact as spoofing.
No verified public proof-of-concept code is available. See the Microsoft Security Update Guide for vendor-supplied technical details.
Detection Methods for CVE-2026-45464
Indicators of Compromise
- SharePoint list items, document properties, or web part configurations containing <script>, javascript:, or HTML event handler attributes such as onerror and onload.
- Outbound HTTP requests from user browsers to unfamiliar domains immediately after rendering SharePoint pages.
- Unexpected modifications to SharePoint content by low-privileged accounts shortly before reports of UI anomalies from other users.
Detection Strategies
- Review SharePoint Unified Logging Service (ULS) logs and audit logs for content updates that include HTML or script tokens in text fields.
- Inspect HTTP responses from SharePoint sites for reflected user input that is not properly encoded.
- Correlate content authoring events from low-privileged users with subsequent page views by administrative accounts.
Monitoring Recommendations
- Enable SharePoint audit logging for item updates, web part edits, and field changes across all site collections.
- Forward SharePoint and IIS logs to a centralized analytics platform for pattern-based detection of script injection attempts.
- Monitor administrator session activity for anomalous requests that originate from rendered SharePoint pages.
How to Mitigate CVE-2026-45464
Immediate Actions Required
- Apply the security update referenced in the Microsoft Security Update Guide for each affected SharePoint Server version.
- Audit existing list items, document properties, and web part configurations for embedded HTML or script content and remove suspicious entries.
- Review SharePoint permissions and remove unnecessary contributor-level access from accounts that do not require it.
Patch Information
Microsoft has published guidance and updates for CVE-2026-45464 through the Microsoft Security Update Guide. Administrators should consult the vendor advisory for the specific cumulative update or security patch applicable to SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Server 2016.
Workarounds
- Restrict content authoring permissions to trusted users until the patch is applied.
- Enforce a strict Content Security Policy (CSP) on SharePoint web applications to limit inline script execution.
- Disable or restrict web parts and field types that accept rich HTML input where business requirements allow.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
