CVE-2025-20234
📋 TL;DR
A memory overread vulnerability in ClamAV's Universal Disk Format (UDF) processing allows unauthenticated remote attackers to cause denial of service by submitting crafted files. This affects systems running vulnerable versions of ClamAV antivirus software, potentially disrupting file scanning services.
💻 Affected Systems
- ClamAV
📦 What is this software?
Clamav by Clamav
⚠️ Risk & Real-World Impact
Worst Case
ClamAV scanning process crashes repeatedly, causing sustained DoS that prevents malware detection and disrupts dependent services like email filtering or file upload scanning.
Likely Case
Intermittent ClamAV process crashes requiring manual restart, temporarily disabling antivirus scanning until service recovery.
If Mitigated
ClamAV crashes but auto-restart mechanisms or monitoring systems quickly restore service with minimal disruption.
🎯 Exploit Status
Exploitation requires only file submission to ClamAV scanning, no authentication needed. Crafted UDF files can trigger the memory overread.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: ClamAV 1.4.3 or 1.0.9
Vendor Advisory: https://blog.clamav.net/2025/06/clamav-143-and-109-security-patch.html
Restart Required: Yes
Instructions:
1. Backup ClamAV configuration. 2. Update using package manager: 'sudo apt update && sudo apt upgrade clamav' (Debian/Ubuntu) or 'sudo yum update clamav' (RHEL/CentOS). 3. Restart ClamAV service: 'sudo systemctl restart clamav-daemon' or equivalent. 4. Verify version with 'clamscan --version'.
🔧 Temporary Workarounds
Disable UDF scanning
linuxTemporarily disable UDF file format scanning in ClamAV configuration to prevent exploitation while patching.
Edit /etc/clamav/clamd.conf
Add line: 'ScanUDF no'
Restart clamd: 'sudo systemctl restart clamav-daemon'
🧯 If You Can't Patch
- Implement network segmentation to restrict file submission to ClamAV from trusted sources only.
- Deploy monitoring and auto-restart for ClamAV processes to minimize DoS impact.
🔍 How to Verify
Check if Vulnerable:
Run 'clamscan --version' and check if version is below 1.4.3 or 1.0.9.Check Version:
clamscan --versionVerify Fix Applied:
Confirm version is 1.4.3 or higher (or 1.0.9+) with 'clamscan --version' and test scanning known safe UDF files.📡 Detection & Monitoring
Log Indicators:
- ClamAV process crashes in system logs
- Repeated ClamAV service restarts
- Error messages related to UDF parsing or memory access
Network Indicators:
- Unusual file upload patterns to systems with ClamAV
- Spikes in file submissions from single sources
SIEM Query:
source="clamav" AND ("crash" OR "segmentation fault" OR "UDF" AND "error")