CVE-2026-23887 Overview
Group-Office is an enterprise customer relationship management (CRM) and groupware tool used by organizations to manage contacts, calendars, projects, and file sharing. A Stored Cross-Site Scripting (XSS) vulnerability has been identified in Group-Office that allows attackers to inject malicious scripts through specially crafted filenames. The application stores unsanitized filenames in the database, which are then rendered without proper encoding when users interact with these files within the application.
Critical Impact
Attackers can interfere with user sessions, steal session cookies, perform unintended actions in the browser on behalf of authenticated users, and potentially compromise sensitive enterprise data within the Group-Office application.
Affected Products
- Group-Office versions 6.8.148 and below
- Group-Office versions 25.0.1 through 25.0.79
Discovery Timeline
- 2026-01-22 - CVE-2026-23887 published to NVD
- 2026-01-22 - Last updated in NVD database
Technical Details for CVE-2026-23887
Vulnerability Analysis
This vulnerability stems from improper input validation (CWE-20) in Group-Office's file handling mechanism. When files are uploaded to the system, the application stores filenames directly in the database without adequate sanitization or encoding. Subsequently, when users view or interact with files through the Group-Office interface, these malicious filenames are rendered in the browser context, executing any embedded JavaScript code.
The attack requires an authenticated user with file upload privileges to craft a malicious filename containing JavaScript payloads. When other users browse or access the file listings, the embedded script executes within their browser session. While the exploitation scope is limited to the file-viewing context, successful attacks can lead to session hijacking, unauthorized actions performed under the victim's identity, and potential data exfiltration within the application boundaries.
Root Cause
The root cause is improper input validation and missing output encoding for user-supplied filenames. The application fails to sanitize special characters and script tags when storing filenames in the database and does not properly encode these values when rendering them in HTML output. This allows HTML and JavaScript content embedded in filenames to be interpreted as executable code rather than displayed as plain text.
Attack Vector
The attack is network-based and requires authenticated access to the application with file upload capabilities. An attacker uploads a file with a specially crafted filename containing malicious JavaScript code. The payload is stored persistently in the database. When legitimate users navigate to file listings or interact with the malicious file entry, the XSS payload executes in their browser within the context of the authenticated session.
The attack mechanism involves embedding script tags or event handlers within the filename string. For example, a filename containing <script> tags or inline event handlers like onerror would be stored verbatim and later rendered without encoding, causing the browser to execute the embedded code. Detailed technical information is available in the GitHub Security Advisory.
Detection Methods for CVE-2026-23887
Indicators of Compromise
- Database entries in file tables containing HTML tags, script elements, or JavaScript event handlers in filename fields
- Unusual filename patterns containing characters like <, >, ", or ' combined with keywords like script, onerror, onload, or onclick
- Web server access logs showing file operations with encoded HTML entities in request parameters
Detection Strategies
- Implement database queries to scan for filenames containing potentially malicious patterns such as <script, javascript:, or HTML event handlers
- Deploy Web Application Firewall (WAF) rules to detect and block file uploads with XSS payloads in filename parameters
- Configure Content Security Policy (CSP) headers to mitigate the impact of XSS by restricting inline script execution
- Review application logs for file upload activities with suspicious filename characteristics
Monitoring Recommendations
- Enable audit logging for all file upload operations and monitor for anomalous filename patterns
- Implement real-time alerting for database inserts containing HTML special characters in filename columns
- Monitor client-side security events through browser reporting mechanisms if CSP violation reporting is enabled
- Conduct periodic security scans of the database for stored XSS indicators in user-generated content fields
How to Mitigate CVE-2026-23887
Immediate Actions Required
- Upgrade Group-Office to version 6.8.149 or 25.0.80 immediately, as these versions contain the security fix
- Audit existing database records for filenames containing suspicious HTML or JavaScript content
- Implement Content Security Policy headers as a defense-in-depth measure while patching is underway
- Restrict file upload permissions to trusted users until the patch is applied
Patch Information
The vulnerability has been fixed in Group-Office versions 6.8.149 and 25.0.80. Organizations should upgrade to these versions or later as soon as possible. The security patches implement proper input sanitization and output encoding for filenames throughout the application.
Relevant commits addressing this issue:
Workarounds
- If immediate patching is not possible, restrict file upload functionality to administrative users only
- Implement server-side filename sanitization at the web server or reverse proxy level to strip HTML and JavaScript content
- Deploy a Web Application Firewall with XSS protection rules to filter malicious payloads in file upload requests
- Consider temporarily disabling file sharing features until the update can be applied
# Example: Add Content-Security-Policy header in Apache configuration
# Add to your Apache configuration or .htaccess file
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none';"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
