CVE-2024-52514
📋 TL;DR
This Nextcloud vulnerability allows users who receive shared folders containing blocked files to copy the intermediate folder structure, potentially bypassing file access controls. It affects Nextcloud Server and Nextcloud Enterprise Server users who utilize file sharing with access restrictions. The issue stems from improper access control when copying folder hierarchies.
💻 Affected Systems
- Nextcloud Server
- Nextcloud Enterprise Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Unauthorized users could access sensitive files that should be blocked by access control rules, potentially exposing confidential data.
Likely Case
Users with legitimate access to shared folders could inadvertently or intentionally bypass file restrictions to access blocked content within those shares.
If Mitigated
With proper access logging and monitoring, unauthorized access attempts could be detected and investigated, though prevention requires patching.
🎯 Exploit Status
Exploitation requires a user account with access to a shared folder containing blocked files. The vulnerability was responsibly disclosed via HackerOne.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Nextcloud Server: 27.1.9, 28.0.5, or 29.0.0; Nextcloud Enterprise Server: 21.0.9.18, 22.2.10.23, 23.0.12.18, 24.0.12.14, 25.0.13.9, 26.0.13.3, 27.1.9, 28.0.5, or 29.0.0
Vendor Advisory: https://github.com/nextcloud/security-advisories/security/advisories/GHSA-g8pr-g25r-58xj
Restart Required: No
Instructions:
1. Backup your Nextcloud instance and database. 2. Update Nextcloud via the web updater (Settings > Overview) or manually download and extract the patched version. 3. Run occ upgrade via command line: sudo -u www-data php occ upgrade. 4. Verify the update completed successfully.
🔧 Temporary Workarounds
Disable file sharing
linuxTemporarily disable file sharing features to prevent exploitation while planning patching.
sudo -u www-data php occ config:app:set files_sharing enabled --value no
Restrict share permissions
linuxReview and tighten share permissions, limiting who can create shares and what can be shared.
sudo -u www-data php occ config:app:set files_sharing default_permissions --value 31
🧯 If You Can't Patch
- Implement strict access control policies and monitor for unusual file access patterns in shared folders.
- Educate users about proper file sharing practices and the risks of copying shared folder structures.
🔍 How to Verify
Check if Vulnerable:
Check your Nextcloud version via the web interface (Settings > Overview) or command line: sudo -u www-data php occ statusCheck Version:
sudo -u www-data php occ status | grep 'versionstring'Verify Fix Applied:
After updating, verify the version matches one of the patched versions listed in the advisory and test that copying shared folders with blocked files no longer bypasses access controls.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns in shared folders
- Multiple copy operations on shared folder structures
- Access attempts to previously blocked files
Network Indicators:
- Increased file transfer activity from users accessing shared folders
SIEM Query:
source="nextcloud.log" ("file copied" OR "folder copied") AND "shared" AND NOT "allowed"