CVE-2026-24906: October CMS Stored XSS Vulnerability

CVE-2026-24906 Overview

October CMS, a popular Content Management System and web platform built on Laravel, contains a Stored Cross-Site Scripting (XSS) vulnerability in the Backend Editor Settings. The Markup Classes fields used for paragraph styles, inline styles, table styles, and other formatting options fail to sanitize input to valid CSS class name characters. When malicious values are entered, they are rendered unsanitized in Froala editor dropdown menus, allowing JavaScript execution when any user opens a RichEditor component.

Critical Impact

Authenticated attackers with editor settings permissions can inject malicious JavaScript that executes when superusers open any RichEditor during routine content editing, potentially leading to privilege escalation and full backend compromise.

Affected Products

• October CMS versions prior to 3.7.14
• October CMS versions prior to 4.1.10
• Installations using the Froala RichEditor with Backend Editor Settings enabled

Discovery Timeline

• April 14, 2026 - CVE-2026-24906 published to NVD
• April 14, 2026 - Last updated in NVD database

Technical Details for CVE-2026-24906

Vulnerability Analysis

This Stored XSS vulnerability (CWE-79) exists within October CMS's Backend Editor Settings functionality. The root issue stems from insufficient input validation in the Markup Classes configuration fields. These fields are designed to accept CSS class names for styling purposes within the Froala rich text editor, but the application fails to enforce proper sanitization or restrict input to valid CSS class name characters.

When an attacker with authenticated backend access and editor settings permissions enters JavaScript code or HTML tags into these fields, the malicious payload is stored server-side. Subsequently, when any user—including superusers with elevated privileges—opens any RichEditor component (such as when editing a blog post or other content), the unsanitized payload is rendered directly into the Froala editor's dropdown menus and executed in the victim's browser context.

The vulnerability requires network access and authenticated backend permissions to exploit, with the attack succeeding when a victim interacts with the compromised editor interface. This attack pattern is particularly dangerous in multi-user CMS environments where lower-privileged editors can target administrators.

Root Cause

The vulnerability originates from missing input sanitization in the Markup Classes fields within October CMS's Backend Editor Settings. The application does not validate that input conforms to valid CSS class name specifications (alphanumeric characters, hyphens, and underscores). Instead, arbitrary strings including HTML and JavaScript are accepted and stored. When the Froala editor constructs its dropdown menus, these unsanitized values are directly interpolated into the DOM without encoding, creating the XSS condition.

Attack Vector

The attack leverages the network-accessible backend interface of October CMS. An authenticated user with permissions to modify editor settings can inject malicious JavaScript payloads into the Markup Classes fields. The stored payload persists in the application's configuration and activates whenever any backend user accesses a RichEditor component.

The exploitation chain follows this pattern: the attacker authenticates to the October CMS backend, navigates to the Editor Settings configuration, injects a malicious script into one of the Markup Classes fields (such as paragraph styles or inline styles), and saves the configuration. When a superuser or administrator subsequently opens any content item that utilizes the RichEditor, the malicious JavaScript executes in their authenticated session context, potentially allowing session hijacking, privilege escalation, or further administrative actions.

Detection Methods for CVE-2026-24906

Indicators of Compromise

• Unusual or suspicious entries in Backend Editor Settings Markup Classes fields containing script tags, event handlers, or encoded JavaScript
• Unexpected JavaScript execution or browser behavior when accessing RichEditor components in the October CMS backend
• Audit logs showing modifications to editor settings by users who should not have such permissions
• Session anomalies or unauthorized administrative actions following RichEditor usage

Detection Strategies

• Review Backend Editor Settings for any Markup Classes entries containing characters beyond valid CSS class names (alphanumeric, hyphens, underscores)
• Implement Content Security Policy (CSP) headers to detect and block inline script execution in the backend interface
• Monitor application logs for editor settings modifications and correlate with user permission levels
• Deploy web application firewalls (WAF) with XSS detection rules targeting the October CMS backend endpoints

Monitoring Recommendations

• Enable detailed audit logging for all Backend Editor Settings changes in October CMS
• Configure alerts for any modifications to editor configuration by non-administrator accounts
• Implement real-time browser security monitoring to detect unexpected script execution in administrative interfaces
• Regularly audit user permissions to ensure only trusted administrators have editor settings access

How to Mitigate CVE-2026-24906

Immediate Actions Required

• Upgrade October CMS to version 3.7.14 or 4.1.10 immediately to apply the security fix
• Audit current Backend Editor Settings Markup Classes fields for any suspicious or non-standard entries
• Restrict editor settings permissions to fully trusted administrators only until patching is complete
• Review user accounts with backend access and remove unnecessary permissions

Patch Information

October CMS has released security patches addressing this vulnerability in versions 3.7.14 (for the 3.x branch) and 4.1.10 (for the 4.x branch). The fix implements proper input sanitization for Markup Classes fields, restricting input to valid CSS class name characters. For detailed technical information about the vulnerability and patch, refer to the GitHub Security Advisory.

Workarounds

• Restrict editor settings permissions to fully trusted administrators only as recommended by the vendor
• Manually audit and sanitize existing Markup Classes field entries, removing any content that does not conform to valid CSS class naming conventions
• Implement network-level access controls to limit backend access to trusted IP addresses
• Consider temporarily disabling RichEditor functionality in high-risk environments until the patch can be applied

# Configuration example
# Verify October CMS version and check for available updates
php artisan october:version
php artisan october:update

# Review current user permissions via artisan console
php artisan backend:user:list

# After updating, clear application cache to ensure new code is active
php artisan cache:clear
php artisan config:clear