CVE-2026-45481: Microsoft SharePoint XSS Vulnerability

CVE-2026-45481 Overview

CVE-2026-45481 is a stored cross-site scripting (XSS) vulnerability in Microsoft Office SharePoint. The flaw stems from improper neutralization of user-supplied input during web page generation [CWE-79]. An authenticated attacker can inject script content that executes in another user's browser session when the page is rendered.

Microsoft classifies the impact as spoofing over a network. Successful exploitation requires user interaction, such as a victim viewing a crafted SharePoint page or item. The vulnerability affects confidentiality and integrity but not availability.

Critical Impact
An authenticated attacker can inject malicious script into SharePoint content to spoof trusted UI, steal session context, or perform actions in the victim's browser session.

Affected Products

Microsoft Office SharePoint (refer to the Microsoft Security Update CVE-2026-45481 advisory for supported version ranges)

Discovery Timeline

2026-06-09 - CVE-2026-45481 published to the National Vulnerability Database
2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-45481

Vulnerability Analysis

The vulnerability is a cross-site scripting flaw in Microsoft Office SharePoint. SharePoint fails to properly neutralize input that is later rendered into a generated web page. An attacker with valid SharePoint credentials can submit input containing script payloads through fields or components that lack sufficient output encoding.

When another user loads the affected page, the browser interprets the injected payload as executable script in the SharePoint origin. The attack requires authentication and user interaction. Because the script runs in the SharePoint security context, the attacker can manipulate page content, impersonate trusted interface elements, and act on behalf of the victim.

Microsoft documents the primary impact as spoofing. This aligns with phishing-style scenarios where injected content alters the displayed UI or initiates requests that appear to originate from a legitimate SharePoint user.

Root Cause

The root cause is missing or insufficient output encoding of attacker-controlled input rendered into HTML responses. SharePoint accepts content from authenticated users and reflects or stores it without consistently applying contextual sanitization, allowing HTML or JavaScript constructs to survive into the final page output [CWE-79].

Attack Vector

The attack vector is network-based and requires low privileges plus user interaction. An authenticated attacker stores or injects script content into a SharePoint location that other users can view. When a victim navigates to the affected page, the payload executes in the victim's browser under the SharePoint origin. EPSS rates the probability of in-the-wild exploitation at 0.064% (20th percentile) as of 2026-06-11.

No verified public proof-of-concept code is available. See the Microsoft Security Update CVE-2026-45481 advisory for vendor-supplied technical detail.

Detection Methods for CVE-2026-45481

Indicators of Compromise

SharePoint list items, document metadata, or page content containing HTML tags such as <script>, <img onerror=...>, or javascript: URIs submitted by standard users.
Outbound browser requests from SharePoint pages to unfamiliar domains, indicating script-driven exfiltration or beaconing.
Audit log entries showing unusual edits to shared SharePoint pages, web parts, or list fields by accounts that do not normally author content.

Detection Strategies

Inspect SharePoint Unified Logging Service (ULS) and audit logs for write operations that include encoded or raw script tokens in user-supplied fields.
Monitor web application firewall and reverse proxy telemetry for HTTP POST bodies to SharePoint endpoints containing script payloads or event handler attributes.
Correlate authenticated content edits with subsequent page views from privileged accounts to identify possible victim exposure.

Monitoring Recommendations

Enable SharePoint auditing for item updates, page edits, and permission changes, and forward logs to a centralized analytics platform.
Alert on Content Security Policy (CSP) violation reports generated by SharePoint front-end pages.
Track anomalous session activity, such as cookie reuse from unexpected IP addresses, following access to recently modified SharePoint pages.

How to Mitigate CVE-2026-45481

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update CVE-2026-45481 advisory to all affected SharePoint servers.
Review SharePoint contributor and editor permissions and remove accounts that do not require write access.
Audit recently modified pages, list items, and web parts for embedded script content and remove suspicious entries.

Patch Information

Microsoft has issued a security update addressing CVE-2026-45481. Administrators should consult the official Microsoft Security Update CVE-2026-45481 entry for the applicable build numbers and deployment guidance for each supported SharePoint version.

Workarounds

Restrict SharePoint authoring privileges to a minimal set of trusted accounts until patching is complete.
Enforce a strict Content Security Policy on SharePoint web applications to limit inline script execution.
Require multi-factor authentication for all SharePoint users to raise the cost of credential-based access needed to exploit the flaw.

bash

# Configuration example: enumerate SharePoint contributors for least-privilege review
Get-SPWeb -Site https://sharepoint.example.com | \
  ForEach-Object { $_.RoleAssignments } | \
  Where-Object { $_.RoleDefinitionBindings.Name -match 'Contribute|Edit|Full Control' } | \
  Select-Object Member, RoleDefinitionBindings