CVE-2024-20505 Overview
A vulnerability exists in the PDF parsing module of Clam AntiVirus (ClamAV) that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on affected devices. The vulnerability stems from an out-of-bounds read condition that occurs when processing specially crafted PDF files, enabling attackers to terminate the scanning process and disrupt antivirus protection.
Critical Impact
Remote attackers can submit malicious PDF files to crash the ClamAV scanning process, potentially leaving systems unprotected against malware during the denial of service condition.
Affected Products
- ClamAV version 1.4.0
- ClamAV versions 1.3.2 and prior
- ClamAV all 1.2.x versions
- ClamAV version 1.0.6 and prior
- ClamAV all 0.105.x versions
- ClamAV all 0.104.x versions
- ClamAV version 0.103.11 and all prior versions
Discovery Timeline
- September 4, 2024 - CVE-2024-20505 published to NVD
- November 3, 2025 - Last updated in NVD database
Technical Details for CVE-2024-20505
Vulnerability Analysis
This vulnerability is classified as CWE-125 (Out-of-Bounds Read), a memory corruption flaw occurring within the PDF parsing module of ClamAV. When the antivirus engine processes PDF documents, it parses the internal structure to extract embedded content for malware analysis. The vulnerable code fails to properly validate buffer boundaries during this parsing operation, allowing reads beyond allocated memory regions.
The attack is remotely exploitable without authentication and requires no user interaction. When a malicious PDF triggers the out-of-bounds read, it causes the ClamAV scanning process to terminate abnormally. This creates a denial of service condition that impacts the availability of the antivirus service while leaving confidentiality and integrity unaffected.
Root Cause
The root cause of CVE-2024-20505 lies in insufficient bounds checking within the PDF parsing module. When ClamAV's libclamav library processes PDF file structures, certain parsing functions do not adequately verify that read operations remain within the bounds of allocated buffers. This allows specially crafted PDF documents with malformed or unexpected structural elements to cause the parser to read memory beyond the intended boundaries, resulting in a crash.
Attack Vector
An attacker can exploit this vulnerability by submitting a crafted PDF file to be scanned by ClamAV. This can occur through multiple attack surfaces:
- Email attachments scanned by mail transfer agents using ClamAV
- File uploads to web applications protected by ClamAV
- Network file shares monitored by ClamAV
- Manual scanning of files from untrusted sources
The exploitation mechanism involves creating a PDF document with malformed structural elements that trigger the out-of-bounds read condition when parsed. Since ClamAV is commonly deployed in automated scanning pipelines, attackers can submit malicious PDFs without direct interaction, making this a practical attack vector against mail servers, web applications, and file servers.
Detection Methods for CVE-2024-20505
Indicators of Compromise
- Unexpected ClamAV process terminations or crashes in system logs
- clamd service restarts occurring without administrator intervention
- Log entries indicating PDF parsing failures or segmentation faults
- Increased frequency of unscanned files in mail queues or file processing pipelines
Detection Strategies
- Monitor ClamAV daemon logs for crash events and unexpected terminations
- Implement process monitoring to detect clamd service interruptions
- Review system logs for segmentation fault signals associated with ClamAV processes
- Configure alerting on ClamAV service availability metrics
Monitoring Recommendations
- Enable verbose logging in ClamAV to capture detailed parsing events
- Configure system monitoring to track clamd process uptime and restart frequency
- Implement mail flow monitoring to detect scanning pipeline disruptions
- Set up automated alerts for ClamAV service health status changes
How to Mitigate CVE-2024-20505
Immediate Actions Required
- Update ClamAV to a patched version immediately (1.4.1, 1.3.2+, 1.0.7, or 0.103.12)
- Review ClamAV service logs for evidence of prior exploitation attempts
- Implement service monitoring to quickly detect and respond to DoS conditions
- Consider temporary workarounds if immediate patching is not possible
Patch Information
ClamAV has released security updates addressing this vulnerability. According to the ClamAV Security Update, the following versions contain the fix:
- ClamAV 1.4.1
- ClamAV 1.3.2 (patched release)
- ClamAV 1.0.7
- ClamAV 0.103.12
Debian users should also refer to the Debian LTS Announcement for distribution-specific update instructions.
Workarounds
- Configure upstream mail filters to quarantine suspicious PDF files before ClamAV scanning
- Implement rate limiting on file submissions to reduce potential DoS impact
- Deploy redundant ClamAV instances to maintain availability during potential attacks
- Enable automatic service restart for clamd to minimize downtime from crashes
# Configuration example - Enable automatic service restart on failure
# Add to systemd service unit for clamd
[Service]
Restart=on-failure
RestartSec=5
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
