CVE-2021-22879
📋 TL;DR
CVE-2021-22879 is a resource injection vulnerability in Nextcloud Desktop Client that allows malicious Nextcloud servers to execute arbitrary commands on users' systems. Users who connect to untrusted Nextcloud servers with vulnerable desktop clients are affected. Exploitation requires user interaction such as clicking a malicious link.
💻 Affected Systems
- Nextcloud Desktop Client
📦 What is this software?
Desktop by Nextcloud
Fedora by Fedoraproject
⚠️ Risk & Real-World Impact
Worst Case
Full remote code execution with the privileges of the logged-in user, potentially leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Limited command execution in user context, potentially stealing local files, installing malware, or accessing sensitive user data.
If Mitigated
No impact if users only connect to trusted Nextcloud servers and have updated to patched versions.
🎯 Exploit Status
Exploitation requires a malicious Nextcloud server and user interaction. Proof-of-concept code is available in public reports.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.1.3 and later
Vendor Advisory: https://nextcloud.com/security/advisory/?id=NC-SA-2021-008
Restart Required: Yes
Instructions:
1. Open Nextcloud Desktop Client. 2. Go to Help > Check for updates. 3. Install version 3.1.3 or later. 4. Restart the client.
🔧 Temporary Workarounds
Disable automatic updates from server
allPrevents the client from processing potentially malicious update URLs from untrusted servers
Not applicable - configure through client settings
Use web interface only
allTemporarily disable the desktop client and access Nextcloud only through web browser
🧯 If You Can't Patch
- Only connect to trusted Nextcloud servers with verified administrators
- Implement network segmentation to isolate Nextcloud client systems from critical assets
🔍 How to Verify
Check if Vulnerable:
Check Help > About in Nextcloud Desktop Client. If version is below 3.1.3, you are vulnerable.Check Version:
nextcloudcmd --version (Linux/macOS) or check About dialog (Windows)Verify Fix Applied:
Confirm version is 3.1.3 or higher in Help > About. Test connection to known-good Nextcloud server.📡 Detection & Monitoring
Log Indicators:
- Unusual process execution from Nextcloud client
- Suspicious command-line arguments in Nextcloud processes
- Failed update attempts from unusual URLs
Network Indicators:
- Nextcloud client connecting to unexpected domains or IPs
- Unusual outbound connections following client-server communication
SIEM Query:
process_name:"nextcloud*" AND (cmdline:"*cmd*" OR cmdline:"*powershell*" OR cmdline:"*bash*" OR cmdline:"*sh*")🔗 References
- https://github.com/nextcloud/desktop/pull/2906
- https://hackerone.com/reports/1078002
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MTWBJAS5DJJIK7LLVBZZQTSJASUVIRVE/
- https://nextcloud.com/security/advisory/?id=NC-SA-2021-008
- https://security.gentoo.org/glsa/202105-37
- https://github.com/nextcloud/desktop/pull/2906
- https://hackerone.com/reports/1078002
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MTWBJAS5DJJIK7LLVBZZQTSJASUVIRVE/
- https://nextcloud.com/security/advisory/?id=NC-SA-2021-008
- https://security.gentoo.org/glsa/202105-37
