CVE-2024-20505 is a vulnerability identified in the PDF parsing module of Clam AntiVirus (ClamAV), a widely used open-source antivirus engine now maintained by Cisco. The flaw exists in multiple versions, including all 1.2.x, 1.3.2, 1.4.0, and earlier releases down to 0.103.0. The root cause is an out-of-bounds read (CWE-125), where the parser reads memory outside the intended buffer when processing crafted PDF files. An attacker can exploit this by submitting a malicious PDF to the ClamAV scanning process, causing it to crash and terminate unexpectedly, resulting in a denial of service (DoS). The vulnerability does not compromise confidentiality or integrity, as it does not allow code execution or data leakage, but it impacts availability by disrupting malware scanning operations. The attack vector is local or adjacent network (AV:L), meaning the attacker must be able to submit files for scanning, but no privileges or user interaction are required. The CVSS v3.1 base score is 4.0 (medium severity), reflecting the limited impact and exploitation complexity. Currently, no patches or known exploits exist, but the vulnerability poses a risk to environments relying on ClamAV for real-time or on-demand scanning, especially where PDF files are frequently processed.

For European organizations, the primary impact is availability degradation of antivirus scanning services, potentially allowing malicious files to bypass detection during downtime. This can affect mail gateways, file servers, and endpoint protection systems that integrate ClamAV for malware scanning. Disruption in scanning may delay threat detection and response, increasing exposure to malware. Organizations in sectors with high reliance on PDF document exchange, such as finance, legal, and government, may face operational interruptions. Additionally, critical infrastructure and managed security service providers using ClamAV appliances could experience service outages. While the vulnerability does not lead to data breaches or system compromise directly, the denial of service could be leveraged as part of multi-stage attacks to weaken defenses. The lack of known exploits reduces immediate risk, but the widespread use of ClamAV in Europe means the vulnerability warrants attention.

European organizations should implement the following mitigations: 1) Restrict or monitor PDF files submitted for scanning, especially from untrusted or external sources, to reduce exposure to crafted malicious PDFs. 2) Deploy ClamAV in isolated or sandboxed environments where possible to limit impact of crashes. 3) Implement redundancy in malware scanning infrastructure to maintain availability if one scanner instance is disrupted. 4) Monitor ClamAV logs and system stability for signs of crashes or abnormal termination. 5) Prepare for timely patching by tracking Cisco advisories and ClamAV updates, as no patches are currently available. 6) Consider alternative or additional antivirus engines for PDF scanning until a fix is released. 7) Educate security teams about this vulnerability to enhance incident detection and response readiness. 8) Limit network access to scanning services to trusted users or systems to reduce attack surface.