CVE-2026-26045: Moodle Backup Restore RCE Vulnerability

CVE-2026-26045 Overview

A code injection vulnerability was identified in Moodle's backup restore functionality where specially crafted backup files are not properly validated during processing. When a malicious backup file is restored, it could lead to unintended execution of server-side code. Since restore capabilities are typically available to privileged users, exploitation requires authenticated access with elevated permissions. Successful exploitation could result in full compromise of the Moodle server, allowing attackers to execute arbitrary code, access sensitive data, and potentially pivot to other systems in the network.

Critical Impact

Authenticated attackers with restore privileges can achieve remote code execution on Moodle servers by uploading and restoring maliciously crafted backup files, leading to complete server compromise.

Affected Products

• Moodle LMS (Learning Management System)
• Moodle Moodle (multiple versions affected)

Discovery Timeline

• 2026-02-21 - CVE-2026-26045 published to NVD
• 2026-02-26 - Last updated in NVD database

Technical Details for CVE-2026-26045

Vulnerability Analysis

This vulnerability falls under CWE-94 (Improper Control of Generation of Code - Code Injection), indicating that the Moodle backup restore functionality fails to properly sanitize or validate the contents of backup files before processing them. The backup restore feature is designed to allow administrators and teachers to migrate course content, user data, and configurations between Moodle instances. However, the lack of proper input validation in the restoration process creates an attack surface where malicious payloads embedded within backup archives can be executed on the server.

The vulnerability requires network access and high-privilege authentication, meaning attackers must first obtain credentials for an account with backup restore capabilities. Common targets include administrator accounts, course managers, or teacher accounts with extended permissions. Once authenticated, the attacker can craft a backup file containing malicious server-side code that executes during the restoration process.

Root Cause

The root cause lies in insufficient validation of backup file contents during the restore operation. Moodle's backup system processes various data types including PHP serialized objects, database queries, and file system operations. When backup files are not thoroughly validated, attackers can inject malicious code that gets executed in the context of the web server. This could include embedded PHP code within data fields, malicious serialized objects that trigger code execution upon deserialization, or carefully crafted file paths that result in arbitrary file writes.

Attack Vector

The attack vector is network-based and requires authenticated access with backup restore privileges. An attacker would follow these steps:

1. Obtain or compromise credentials for a privileged Moodle account (administrator, course creator, or teacher with restore capabilities)
2. Craft a malicious backup file (.mbz format) containing embedded code injection payloads
3. Upload the malicious backup file through Moodle's restore interface
4. Initiate the restore process, triggering execution of the malicious code
5. Achieve remote code execution on the underlying server

The vulnerability exploits the trust relationship between the backup file format and the restore processing logic. Since backup files are typically created by trusted users within the same system, the restore function may not apply the same level of scrutiny that would be applied to untrusted external input.

Detection Methods for CVE-2026-26045

Indicators of Compromise

• Unexpected backup restore operations from unusual IP addresses or at unusual times
• Modified or newly created PHP files in the Moodle installation directory after restore operations
• Web server processes spawning unusual child processes or shell commands
• Anomalous outbound network connections from the Moodle server
• Presence of backup files with suspicious or obfuscated content

Detection Strategies

• Monitor Moodle audit logs for backup restore operations, especially from newly created or recently compromised accounts
• Implement file integrity monitoring (FIM) on the Moodle installation directory to detect unauthorized file changes
• Deploy web application firewall (WAF) rules to inspect backup file uploads for known malicious patterns
• Analyze web server logs for unusual POST requests to restore endpoints with large payloads
• Configure SIEM alerts for backup restore events followed by suspicious server-side activity

Monitoring Recommendations

• Enable verbose logging for all backup and restore operations in Moodle
• Implement real-time alerting for any restore operations performed by non-administrative users
• Monitor for webshell indicators and reverse shell connections from the Moodle server
• Track process execution chains originating from web server processes (Apache/Nginx)
• Review backup file metadata and checksums before allowing restore operations

How to Mitigate CVE-2026-26045

Immediate Actions Required

• Restrict backup restore permissions to only essential administrative personnel
• Audit current accounts with restore capabilities and remove unnecessary privileges
• Enable multi-factor authentication (MFA) for all administrator accounts
• Review recent backup restore operations for any suspicious activity
• Consider temporarily disabling the restore functionality until patches are applied

Patch Information

Administrators should consult official Moodle security advisories and apply the latest security patches as soon as they become available. For additional information and patch details, refer to the Red Hat CVE-2026-26045 Advisory and the Red Hat Bugzilla Report #2440901. Organizations using Moodle packages from Linux distributions should check their respective security update channels.

Workarounds

• Implement strict role-based access control limiting backup restore to a minimal set of trusted administrators
• Deploy a web application firewall (WAF) to inspect and potentially block suspicious backup file uploads
• Isolate the Moodle server in a network segment with restricted outbound access to limit post-exploitation impact
• Enable Moodle's built-in backup validation features if available in your version
• Consider implementing an out-of-band approval workflow for backup restore operations

# Restrict restore capability to admin role only in Moodle
# Access: Site administration > Users > Permissions > Define roles
# Remove 'moodle/restore:*' capabilities from non-admin roles

# Monitor Moodle logs for restore operations
tail -f /var/www/moodledata/logstore_standard/standard.log | grep -i restore

# Check for recently modified PHP files (potential webshells)
find /var/www/moodle -name "*.php" -mtime -1 -ls