CVE-2021-40219
📋 TL;DR
Bolt CMS versions up to 4.2 contain a server-side template injection vulnerability in theme rendering functionality. Authenticated attackers can edit themes to inject malicious templates, leading to remote code execution on the server. This affects all Bolt CMS installations running vulnerable versions with authenticated user access.
💻 Affected Systems
- Bolt CMS
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise allowing attacker to execute arbitrary commands, access sensitive data, install malware, or pivot to other systems.
Likely Case
Attacker gains shell access to the web server, potentially compromising the entire Bolt CMS installation and underlying server.
If Mitigated
Limited impact if proper authentication controls and input validation are in place, though authenticated users could still exploit.
🎯 Exploit Status
Exploit requires authenticated access. Public proof-of-concept code is available in GitHub repositories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.2.1 and later
Vendor Advisory: https://github.com/bolt/core/security/advisories
Restart Required: No
Instructions:
1. Backup your Bolt CMS installation and database. 2. Update to Bolt CMS 4.2.1 or later via composer: 'composer require bolt/core:^4.2.1'. 3. Clear cache: 'php bin/console cache:clear'. 4. Verify the update completed successfully.
🔧 Temporary Workarounds
Restrict Theme Editing Permissions
allTemporarily disable theme editing for all non-admin users until patching can be completed.
Edit Bolt CMS configuration to remove 'theme' editing permissions from user roles
Implement Web Application Firewall Rules
allBlock template injection patterns in theme editing requests.
Configure WAF to block requests containing template injection patterns like {{, {% in theme edit requests
🧯 If You Can't Patch
- Restrict access to Bolt CMS admin interface to trusted IP addresses only
- Implement strict user role management and audit all users with theme editing permissions
🔍 How to Verify
Check if Vulnerable:
Check Bolt CMS version in admin panel or via composer: 'composer show bolt/core | grep version'Check Version:
composer show bolt/core | grep versionVerify Fix Applied:
Confirm version is 4.2.1 or higher and test theme editing functionality for proper input validation📡 Detection & Monitoring
Log Indicators:
- Unusual theme file modifications
- Template syntax in theme edit requests
- Multiple failed theme edit attempts
Network Indicators:
- POST requests to theme editing endpoints with template injection patterns
- Unusual outbound connections from web server
SIEM Query:
source="bolt_cms.logs" AND ("theme/edit" OR "templatecontroller") AND ("{{" OR "{%" OR "%}" OR "}}")🔗 References
- http://boltcms.com
- https://github.com/bolt/core
- https://github.com/bolt/core/blob/3b21a73ebf519b76756d3ad2841312d10ef11461/src/Controller/Frontend/TemplateController.php
- https://github.com/iiSiLvEr/CVEs/tree/main/CVE-2021-40219
- http://boltcms.com
- https://github.com/bolt/core
- https://github.com/bolt/core/blob/3b21a73ebf519b76756d3ad2841312d10ef11461/src/Controller/Frontend/TemplateController.php
- https://github.com/iiSiLvEr/CVEs/tree/main/CVE-2021-40219
