CVE-2025-20234: ClamAV UDF Processing DoS Vulnerability

CVE-2025-20234 Overview

A vulnerability in Universal Disk Format (UDF) processing of ClamAV could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to a memory overread during UDF file scanning. An attacker could exploit this vulnerability by submitting a crafted file containing UDF content to be scanned by ClamAV on an affected device. A successful exploit could allow the attacker to terminate the ClamAV scanning process, resulting in a DoS condition on the affected software.

Critical Impact

Unauthenticated remote attackers can crash the ClamAV scanning process by submitting maliciously crafted UDF files, disrupting malware protection services across affected systems including Cisco Secure Endpoint deployments.

Affected Products

• ClamAV (all vulnerable versions)
• Cisco Secure Endpoint (Linux, macOS, and Windows)
• Cisco Secure Endpoint Private Cloud

Discovery Timeline

• 2025-06-18 - CVE-2025-20234 published to NVD
• 2025-08-11 - Last updated in NVD database

Technical Details for CVE-2025-20234

Vulnerability Analysis

CVE-2025-20234 is classified as an Out-of-Bounds Read vulnerability (CWE-125) that affects the Universal Disk Format (UDF) file parsing functionality within ClamAV. The vulnerability occurs when the ClamAV engine processes specially crafted UDF content, triggering a memory overread condition that causes the scanning process to crash.

The UDF file system format is commonly used for optical media such as DVDs and Blu-ray discs, as well as disk images. During the scanning process, ClamAV parses UDF structures to detect potential malware hidden within these file formats. The vulnerability exists in how the scanner handles malformed or boundary-exceeding data within UDF structures, leading to reading memory beyond allocated buffers.

This vulnerability is particularly concerning in enterprise environments where ClamAV serves as a critical component of email gateways, file servers, or endpoint protection solutions. A successful attack does not compromise data confidentiality or integrity but can effectively disable malware scanning capabilities, leaving systems temporarily unprotected.

Root Cause

The root cause of this vulnerability is improper bounds checking during the parsing of Universal Disk Format structures within the ClamAV engine. When processing UDF content, the scanner fails to properly validate the length or offset values within the file format structures before reading memory. This allows a crafted file to specify values that cause the scanner to read beyond the allocated buffer boundaries, resulting in an out-of-bounds read condition that triggers a crash.

Attack Vector

The attack can be executed remotely without authentication by delivering a maliciously crafted file to any system running vulnerable ClamAV versions. Attack vectors include:

• Sending malicious email attachments that trigger automatic scanning
• Uploading crafted files to web applications protected by ClamAV
• Placing malicious files on network shares monitored by ClamAV
• Submitting UDF disk images or files containing UDF content to scanning endpoints

The attack requires no user interaction beyond the normal file scanning process. Once the crafted UDF content is processed by ClamAV, the memory overread occurs, causing the scanning daemon to terminate unexpectedly.

Detection Methods for CVE-2025-20234

Indicators of Compromise

• Unexpected termination or crashes of clamd or clamscan processes
• Service restart events for ClamAV-related services in system logs
• Presence of malformed UDF files or disk images in scan queues
• Segmentation fault or memory access violation errors in ClamAV logs

Detection Strategies

• Monitor ClamAV process stability and implement alerting for unexpected daemon restarts
• Implement file type detection at network boundaries to identify UDF content before it reaches scanning engines
• Review system logs for crash dumps or core files associated with ClamAV processes
• Deploy network-based intrusion detection signatures for known malicious UDF patterns

Monitoring Recommendations

• Configure centralized logging for all ClamAV instances to track service availability
• Implement watchdog processes to automatically restart ClamAV services after crashes while alerting administrators
• Monitor for repeated crash-restart cycles that may indicate active exploitation attempts
• Track scan failure rates and processing errors as potential indicators of attack

How to Mitigate CVE-2025-20234

Immediate Actions Required

• Update ClamAV to version 1.4.3, 1.0.9, or later as specified in the ClamAV Security Patch Announcement
• Update Cisco Secure Endpoint to the latest available version for your platform
• Update Cisco Secure Endpoint Private Cloud to address this vulnerability
• Verify ClamAV service health after applying updates to confirm successful patching

Patch Information

ClamAV has released security patches addressing this vulnerability in versions 1.4.3 and 1.0.9. Organizations should update to these versions or later to remediate the vulnerability. For Cisco Secure Endpoint deployments, consult the Cisco Security Advisory for specific version guidance.

Detailed patch information and release notes are available in the ClamAV Security Patch Announcement.

Workarounds

• Implement file filtering at network perimeters to quarantine or block UDF files before they reach ClamAV
• Configure automatic service restart policies to minimize downtime if exploitation occurs
• Deploy redundant scanning infrastructure to maintain protection during potential service disruptions
• Consider temporarily disabling UDF scanning if patches cannot be immediately applied (note: this reduces detection capabilities)

# Verify ClamAV version after patching
clamscan --version

# Check ClamAV service status
systemctl status clamav-daemon

# Review ClamAV logs for crash events
journalctl -u clamav-daemon --since "24 hours ago" | grep -i "error\|crash\|fault"