CVE-2020-21522
📋 TL;DR
CVE-2020-21522 is a Zip Slip directory traversal vulnerability in Halo CMS version 1.1.3 that allows attackers to overwrite critical system files through malicious archive uploads. This affects all systems running the vulnerable Halo version, potentially leading to remote code execution. Attackers can gain operating system permissions by overwriting files like .bashrc or template files.
💻 Affected Systems
- Halo CMS
📦 What is this software?
Halo by Halo
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining root/administrator privileges, complete data loss, and persistent backdoor installation.
Likely Case
Remote code execution leading to web server compromise, data exfiltration, and lateral movement within the network.
If Mitigated
Limited impact with proper file permission restrictions and network segmentation preventing system-wide compromise.
🎯 Exploit Status
Exploitation requires backend access to upload files. The vulnerability is well-documented in the GitHub issues with technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 1.1.4 or later
Vendor Advisory: https://github.com/halo-dev/halo/issues/418
Restart Required: Yes
Instructions:
1. Backup your Halo installation and database. 2. Download Halo version 1.1.4 or later from the official repository. 3. Replace the existing installation with the patched version. 4. Restart the Halo service or web server.
🔧 Temporary Workarounds
Disable file upload functionality
allTemporarily disable file upload features in the Halo backend until patching is possible.
# Modify Halo configuration to disable uploads
# Check configuration files for upload settings
Implement strict file upload validation
allAdd server-side validation to reject archives containing path traversal sequences.
# Implement file validation in upload handlers
# Add checks for '../' and similar sequences in filenames
🧯 If You Can't Patch
- Implement strict file system permissions to prevent overwriting critical system files
- Deploy network segmentation to isolate the Halo instance from sensitive systems
🔍 How to Verify
Check if Vulnerable:
Check the Halo version by examining the application files or configuration. Version 1.1.3 is vulnerable.Check Version:
Check the version in Halo admin panel or examine package.json/application.properties filesVerify Fix Applied:
Verify the installation is running Halo version 1.1.4 or later and test file upload functionality with traversal attempts.📡 Detection & Monitoring
Log Indicators:
- Unusual file upload attempts with path traversal sequences
- Failed attempts to access system files from web context
- Unexpected file modifications in system directories
Network Indicators:
- Large archive uploads to Halo backend endpoints
- Unusual outbound connections from the Halo server
SIEM Query:
source="halo.logs" AND ("../" OR "..\\" OR "%2e%2e%2f") AND action="upload"