CVE-2024-20505: ClamAV PDF Parsing DoS Vulnerability

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

bash

# Configuration example - Enable automatic service restart on failure
# Add to systemd service unit for clamd
[Service]
Restart=on-failure
RestartSec=5