CVE-2025-67851: Moodle Formula Injection Vulnerability

CVE-2025-67851 Overview

A formula injection vulnerability has been identified in Moodle, a widely-used open-source learning management system (LMS). This flaw occurs when data fields are exported without proper escaping, allowing a remote attacker to inject malicious formulas into exported data. When the exported file is opened in a spreadsheet application such as Microsoft Excel or Google Sheets, the embedded formulas execute, potentially leading to compromised data integrity and unintended operations within the spreadsheet environment.

Critical Impact

Attackers can exploit improper data export sanitization to inject malicious spreadsheet formulas, enabling data exfiltration, credential theft, or arbitrary command execution when victims open exported files in spreadsheet applications.

Affected Products

• Moodle LMS (specific versions not disclosed in advisory)
• Systems utilizing Moodle data export functionality
• Organizations relying on exported Moodle data in spreadsheet applications

Discovery Timeline

• 2026-02-03 - CVE-2025-67851 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2025-67851

Vulnerability Analysis

This vulnerability is classified as CWE-1236 (Improper Neutralization of Formula Elements in a CSV File), commonly known as CSV Injection or Formula Injection. The flaw exists in how Moodle processes and exports user-supplied data to external file formats such as CSV or other spreadsheet-compatible formats.

When a user exports data from Moodle (such as user profiles, grades, or other database content), the application fails to properly sanitize or escape special characters that are interpreted as formula delimiters by spreadsheet applications. Characters like =, +, -, @, and tab characters at the beginning of cell values can trigger formula execution in applications like Microsoft Excel, Google Sheets, or LibreOffice Calc.

An attacker with the ability to submit data to Moodle (such as through user profile fields, assignment submissions, or forum posts) can craft malicious payloads that remain dormant within the database until an administrator or instructor exports the data. Upon opening the exported file, the spreadsheet application interprets the payload as a formula and executes it.

Root Cause

The root cause lies in insufficient output encoding during the data export process. When Moodle generates exportable data, it does not properly escape or prefix cell values that begin with characters recognized as formula indicators by spreadsheet applications. This allows user-controlled input to break out of the data context and be interpreted as executable formulas.

Proper mitigation requires either prefixing potentially dangerous cell values with a single quote character (') to force text interpretation, or implementing comprehensive output encoding that neutralizes formula injection vectors.

Attack Vector

The attack requires local access in the sense that the attacker must have legitimate access to submit data into Moodle fields that may later be exported. The exploitation chain involves:

1. Initial Access: Attacker submits malicious formula-containing data through legitimate Moodle input channels (profile fields, course enrollments, forum posts, etc.)
2. Persistence: The malicious payload is stored in the Moodle database without triggering any alerts
3. Trigger: An administrator or instructor with export privileges exports data containing the attacker's payload
4. Execution: The victim opens the exported file in a spreadsheet application, causing the malicious formula to execute

Common payload examples include Dynamic Data Exchange (DDE) formulas that can execute system commands or formulas that exfiltrate data to attacker-controlled servers. The vulnerability requires user interaction (opening the exported file) and operates within the security context of the victim's spreadsheet application.

For technical details regarding the vulnerability mechanism, refer to the Moodle Forum Discussion and the Red Hat CVE Advisory.

Detection Methods for CVE-2025-67851

Indicators of Compromise

• Presence of formula injection payloads in Moodle database fields (values beginning with =, +, -, @, or containing DDE commands like =cmd|)
• User-submitted content containing suspicious patterns such as =HYPERLINK(), =IMPORTXML(), =WEBSERVICE(), or DDE sequences
• Log entries indicating unusual data submissions with special characters in profile or course data fields
• Reports from users about unexpected behavior when opening exported Moodle data files

Detection Strategies

• Implement database scanning for cells containing formula injection patterns such as ^[=+\-@] or DDE command syntax
• Deploy web application firewall (WAF) rules to detect and block formula injection payloads in incoming POST requests
• Monitor Moodle audit logs for suspicious data submissions, particularly in fields commonly included in exports
• Configure endpoint detection to alert on spreadsheet applications executing commands or making unusual network connections after opening CSV/Excel files

Monitoring Recommendations

• Enable verbose logging for Moodle data export operations to track who exports data and what datasets are included
• Implement file integrity monitoring for exported files if they are stored on shared network locations
• Configure SIEM rules to correlate Moodle export activities with subsequent endpoint alerts
• Regularly audit user-submitted data in Moodle for suspicious patterns that could indicate attempted exploitation

How to Mitigate CVE-2025-67851

Immediate Actions Required

• Review and apply security patches from Moodle when available by monitoring the Moodle Forum Discussion
• Audit existing Moodle database content for potential formula injection payloads in user-submitted fields
• Educate administrators and instructors about the risks of opening exported data in spreadsheet applications
• Consider implementing administrative controls to limit data export capabilities to trusted users only
• Enable Protected View or similar sandboxing features in spreadsheet applications used to open exported Moodle data

Patch Information

Patch information is available through the official Moodle security channels. Organizations should consult the Moodle Forum Discussion for the latest updates on patched versions. Additional technical details are available in Red Hat Bug Report #2423841.

Workarounds

• Configure spreadsheet applications to disable automatic formula execution and DDE features before opening exported Moodle files
• Pre-process exported files using scripts that prefix all cell values with single quotes to force text interpretation
• Use text editors instead of spreadsheet applications to review exported data when formula execution is not required
• Implement input validation on Moodle data fields to reject or sanitize values beginning with formula indicator characters

# Configuration example - Disable DDE in Microsoft Excel via registry
# Run as administrator on Windows systems opening Moodle exports
reg add "HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Excel\Security" /v WorkbookLinkWarnings /t REG_DWORD /d 2 /f

# Pre-processing script example - Add single quote prefix to CSV cells
# This forces text interpretation and prevents formula execution
sed -i "s/^\([=+\-@]\)/'\1/g; s/,\([=+\-@]\)/,'\1/g" exported_data.csv