CVE-2025-26525: Moodle Path Traversal Vulnerability

CVE-2025-26525 Overview

CVE-2025-26525 is a critical arbitrary file read vulnerability affecting Moodle's TeX notation filter. The vulnerability stems from insufficient input sanitization when processing TeX notation, allowing unauthenticated attackers to read arbitrary files from the server on systems where pdfTeX is available (such as those with TeX Live installed).

This vulnerability falls under CWE-552 (Files or Directories Accessible to External Parties), representing a serious information disclosure risk that could expose sensitive configuration files, credentials, and other confidential data stored on affected Moodle servers.

Critical Impact

Unauthenticated attackers can read arbitrary files from Moodle servers where TeX Live is installed, potentially exposing sensitive configuration data, database credentials, and other confidential information.

Affected Products

• Moodle LMS (multiple versions with TeX notation filter enabled)
• Systems with pdfTeX available (TeX Live installations)
• Moodle instances using the TeX notation filter for mathematical content rendering

Discovery Timeline

• 2025-02-24 - CVE-2025-26525 published to NVD
• 2025-08-08 - Last updated in NVD database

Technical Details for CVE-2025-26525

Vulnerability Analysis

The vulnerability exists within Moodle's TeX notation filter, a component designed to render mathematical formulas and expressions. When processing user-supplied TeX input, the filter fails to properly sanitize special commands that can be leveraged to read files from the underlying file system.

The attack is network-accessible and requires no authentication or user interaction, making it particularly dangerous for internet-facing Moodle installations. The scope change indicator in the vulnerability assessment suggests that successful exploitation could impact resources beyond the vulnerable component itself.

This vulnerability specifically affects environments where pdfTeX is available, typically through TeX Live installations. TeX Live is commonly installed on educational platforms to support mathematical content rendering, meaning many Moodle deployments in academic environments are potentially at risk.

Root Cause

The root cause of CVE-2025-26525 is insufficient sanitization of user-supplied input in the TeX notation filter. The filter processes TeX commands without adequately validating or restricting commands that can access the file system. TeX engines like pdfTeX include powerful primitives such as \input, \openin, and related commands that can read external files during document processing.

Without proper filtering, an attacker can craft malicious TeX input that instructs pdfTeX to read arbitrary files from the server and include their contents in the rendered output, effectively exfiltrating sensitive data.

Attack Vector

The attack can be executed remotely over the network without authentication. An attacker would craft malicious TeX notation containing file-reading primitives and submit it through any Moodle interface that processes TeX content.

The exploitation flow involves:

1. Identifying a Moodle instance with the TeX notation filter enabled
2. Crafting malicious TeX input containing file read commands
3. Submitting the payload through a content input field (e.g., forum posts, assignments, or other user-generated content areas)
4. The pdfTeX processor executes the commands and reads the targeted files
5. File contents are returned in the rendered output or error messages

Targeted files may include /etc/passwd, Moodle's config.php containing database credentials, or other sensitive system and application files.

Detection Methods for CVE-2025-26525

Indicators of Compromise

• Unusual TeX processing errors in Moodle logs referencing file paths outside expected directories
• pdfTeX processes accessing sensitive system files like /etc/passwd or config.php
• Anomalous content submissions containing TeX primitives such as \input, \openin, \read, or \write
• Unexpected file access patterns from the web server user account

Detection Strategies

• Monitor Moodle application logs for TeX filter processing errors or unusual file path references
• Implement Web Application Firewall (WAF) rules to detect TeX file-reading primitives in POST data
• Review pdfTeX process activity for access to files outside the Moodle data directory
• Audit content submissions for suspicious TeX command patterns

Monitoring Recommendations

• Enable verbose logging for the TeX notation filter component
• Monitor file access patterns from the web server process, particularly to configuration files
• Set up alerts for pdfTeX processes accessing files outside the TeX Live installation directory
• Review Moodle access logs for repeated requests to content rendering endpoints

How to Mitigate CVE-2025-26525

Immediate Actions Required

• Apply the official Moodle security patch referenced in MDL-84136 immediately
• If patching is not immediately possible, disable the TeX notation filter until updates can be applied
• Review server logs for potential exploitation attempts
• Audit any potentially exposed credentials and rotate them if compromise is suspected

Patch Information

Moodle has released patches to address this vulnerability. The fix is tracked under MDL-84136 and is available through the official Moodle Git repository. Administrators should update to the latest patched version of their Moodle branch.

For detailed patch information and commit history, refer to the Moodle Commit MDL-84136. Additional discussion and context can be found in the Moodle Forum Discussion.

Workarounds

• Disable the TeX notation filter in Site Administration → Plugins → Filters → Manage filters
• If TeX rendering is required, consider using alternative rendering methods like MathJax that don't rely on pdfTeX
• Implement filesystem-level restrictions on the pdfTeX binary to prevent access to sensitive directories
• Use a containerized or sandboxed environment for TeX processing to limit file system access

# Disable TeX notation filter via Moodle CLI
php admin/cli/cfg.php --name=textfilters --set="tex=0"

# Alternatively, restrict pdfTeX file access using AppArmor (example profile addition)
# Add to /etc/apparmor.d/usr.bin.pdflatex
deny /etc/passwd r,
deny /var/www/moodle/config.php r,