CVE-2026-26047: Moodle TeX Editor DOS Vulnerability

CVE-2026-26047 Overview

A denial-of-service vulnerability was identified in Moodle's TeX formula editor. When rendering TeX content using mimetex, insufficient execution time limits could allow specially crafted formulas to consume excessive server resources. An authenticated user could abuse this behavior to degrade performance or cause service interruption.

This vulnerability affects Moodle learning management system deployments that utilize the TeX formula editor component. The flaw stems from inadequate resource controls when processing complex mathematical formulas, making it possible for malicious actors to craft formulas that monopolize server CPU and memory resources.

Critical Impact

Authenticated attackers can craft malicious TeX formulas to exhaust server resources, potentially causing widespread service disruption for all Moodle users on the affected instance.

Affected Products

• Moodle LMS (multiple versions)
• Moodle mimetex integration
• Moodle TeX formula editor component

Discovery Timeline

• 2026-02-21 - CVE-2026-26047 published to NVD
• 2026-02-26 - Last updated in NVD database

Technical Details for CVE-2026-26047

Vulnerability Analysis

This denial-of-service vulnerability exists within Moodle's TeX formula rendering functionality. The mimetex component, responsible for converting TeX mathematical notation into rendered images, lacks adequate execution time limits and resource constraints. When processing TeX formulas, the system does not properly bound the computational complexity that can be introduced through specially crafted input.

The vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption) and CWE-770 (Allocation of Resources Without Limits or Throttling), indicating that the core issue involves insufficient controls over how much processing time and memory can be consumed during formula rendering operations.

Root Cause

The root cause of this vulnerability is the absence of proper execution time limits and resource allocation controls within the mimetex formula processing engine. When a user submits a TeX formula for rendering, the system processes it without adequate safeguards to prevent computationally expensive operations from monopolizing server resources.

The mimetex component processes formulas in a manner that allows certain complex or recursive mathematical expressions to trigger excessive processing cycles. Without enforced timeouts or resource caps, these operations can run unbounded, effectively starving other processes of CPU time and memory.

Attack Vector

The attack vector for this vulnerability requires network access and low-privilege authentication. An attacker must have a valid Moodle account with permissions to submit TeX formulas, which is commonly available to students, instructors, and other authenticated users.

The attack is executed by submitting specially crafted TeX formulas through any Moodle interface that supports mathematical notation, such as:

• Forum posts with embedded equations
• Quiz questions containing mathematical content
• Assignment submissions with formula markup
• Course content pages with TeX notation

The malicious formula is designed to maximize computational complexity, causing the mimetex rendering process to consume excessive CPU cycles and memory. Repeated submissions or multiple concurrent requests can amplify the impact, potentially bringing the entire Moodle instance to a halt.

Due to the nature of this vulnerability, specific exploitation code is not provided. The attack leverages legitimate TeX formula submission functionality with carefully constructed input designed to maximize processing overhead. Security researchers should refer to the Red Hat Bug Report #2440905 for additional technical details.

Detection Methods for CVE-2026-26047

Indicators of Compromise

• Abnormally high CPU utilization on web servers hosting Moodle, particularly in mimetex-related processes
• Increased memory consumption correlated with TeX formula rendering requests
• Slow response times or timeouts when accessing Moodle pages with mathematical content
• Repeated TeX formula submission requests from individual user accounts
• Web server logs showing numerous requests to formula rendering endpoints

Detection Strategies

• Monitor server resource utilization for anomalous spikes in CPU and memory usage during formula rendering operations
• Implement application-level logging to track TeX formula submission frequency and identify potential abuse patterns
• Configure alerting thresholds for mimetex process execution times that exceed normal operational parameters
• Deploy SentinelOne Singularity to detect and alert on resource exhaustion attack patterns

Monitoring Recommendations

• Establish baseline metrics for normal TeX formula processing times and resource consumption
• Configure real-time alerts for processes exceeding defined execution time thresholds
• Monitor Moodle application logs for unusual patterns in formula submission activity
• Implement user behavior analytics to identify accounts exhibiting potential DoS attack behavior

How to Mitigate CVE-2026-26047

Immediate Actions Required

• Apply the latest security patches from Moodle as they become available
• Implement execution time limits on the mimetex rendering process at the server level
• Consider temporarily disabling the TeX formula editor if not essential for operations
• Review and restrict user permissions for submitting TeX content where appropriate
• Enable rate limiting on formula submission endpoints

Patch Information

Organizations should monitor Moodle's official security announcements for patches addressing this vulnerability. Additional information is available through the Red Hat Security Advisory and Red Hat Bug Report #2440905.

Administrators should update to patched Moodle versions as soon as they are released and verify the update was successful by checking the version information in the Moodle administration panel.

Workarounds

• Configure PHP execution time limits specifically for mimetex processing scripts
• Implement process-level resource controls using operating system tools like ulimit or cgroups
• Deploy a web application firewall (WAF) with rules to detect and block malicious TeX formula patterns
• Enable rate limiting at the reverse proxy or load balancer level to throttle formula submission requests
• Consider using an alternative TeX rendering solution with built-in resource constraints

# Example PHP configuration to limit execution time for mimetex
# Add to php.ini or .htaccess for the mimetex directory
max_execution_time = 30
memory_limit = 128M

# Example Apache configuration for rate limiting
<Location "/filter/tex/">
    SetEnvIf Request_URI "mimetex" rate_limit
    LimitRequestBody 10240
</Location>