CVE-2023-26482
📋 TL;DR
This vulnerability in Nextcloud server allows non-admin users to create workflows that should be restricted to administrators. Since some workflows can execute scripts on the server, this can lead to remote code execution (RCE). All Nextcloud instances with affected versions and the workflow apps enabled are vulnerable.
💻 Affected Systems
- Nextcloud Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise via remote code execution, allowing attackers to execute arbitrary commands, access sensitive data, and potentially pivot to other systems.
Likely Case
Privilege escalation where authenticated users gain administrative capabilities and execute scripts on the server, potentially leading to data theft or further system compromise.
If Mitigated
Limited impact with proper access controls and monitoring, potentially only allowing workflow creation but not script execution if those apps are disabled.
🎯 Exploit Status
Exploitation requires authenticated user access but is straightforward once authenticated. The vulnerability is well-documented in public advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 24.0.10 or 25.0.4
Vendor Advisory: https://github.com/nextcloud/security-advisories/security/advisories/GHSA-h3c9-cmh8-7qpj
Restart Required: Yes
Instructions:
1. Backup your Nextcloud instance and database. 2. Update Nextcloud via the web updater or manually download and extract the patched version. 3. Run occ upgrade via command line. 4. Restart your web server and PHP-FPM services.
🔧 Temporary Workarounds
Disable vulnerable workflow apps
linuxDisable the workflow_scripts and workflow_pdf_converter apps to prevent script execution capabilities
sudo -u www-data php occ app:disable workflow_scripts
sudo -u www-data php occ app:disable workflow_pdf_converter
🧯 If You Can't Patch
- Disable workflow_scripts and workflow_pdf_converter apps immediately
- Implement strict access controls and monitor for unauthorized workflow creation attempts
🔍 How to Verify
Check if Vulnerable:
Check Nextcloud version via admin panel or run: sudo -u www-data php occ statusCheck Version:
sudo -u www-data php occ status | grep 'versionstring'Verify Fix Applied:
Confirm version is 24.0.10 or higher (for v24) or 25.0.4 or higher (for v25)📡 Detection & Monitoring
Log Indicators:
- Unauthorized workflow creation attempts
- Unexpected script execution via workflow apps
- User privilege escalation patterns
Network Indicators:
- Unusual outbound connections from Nextcloud server
- Suspicious POST requests to workflow endpoints
SIEM Query:
source="nextcloud.log" AND ("workflow_scripts" OR "workflow_pdf_converter") AND ("created" OR "executed")🔗 References
- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-h3c9-cmh8-7qpj
- https://github.com/nextcloud/server/commit/5a06b50b10cc9278bbe68bbf897a0c4aeb0c4e60
- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-h3c9-cmh8-7qpj
- https://github.com/nextcloud/server/commit/5a06b50b10cc9278bbe68bbf897a0c4aeb0c4e60
