CVE-2006-5874 in ClamAV
Summary
by MITRE
Clam AntiVirus (ClamAV) 0.88 and earlier allows remote attackers to cause a denial of service (crash) via a malformed base64-encoded MIME attachment that triggers a null pointer dereference.
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Analysis
by VulDB Data Team • 02/03/2025
ClamAV version 0.88 and earlier contains a critical vulnerability that enables remote attackers to execute a denial of service attack through carefully crafted malformed base64-encoded MIME attachments. This vulnerability stems from inadequate input validation within the email scanning functionality where the software fails to properly handle malformed base64 encoding sequences. The flaw manifests as a null pointer dereference condition that occurs when the scanner attempts to process attachment data that does not conform to expected MIME encoding standards. When such malformed data is encountered during the scanning process, the application crashes due to attempting to access memory at a null pointer location, resulting in complete service disruption.
The technical nature of this vulnerability aligns with CWE-476 which describes null pointer dereference conditions in software implementations. This weakness represents a classic memory safety issue where the program assumes that certain pointers contain valid memory addresses without proper validation. The attack vector specifically targets the email content processing module where base64-encoded attachments are parsed and analyzed for malicious content. The vulnerability is particularly concerning because it can be triggered remotely through email transmission, making it exploitable in real-world scenarios where users receive email messages containing crafted attachments. The impact extends beyond simple service interruption as it can potentially be used to disrupt email services or create conditions where legitimate email traffic is blocked or delayed.
From an operational standpoint, this vulnerability creates significant risk for organizations relying on ClamAV for email security filtering. The remote exploit capability means that attackers can target systems without requiring physical access or local network presence, making it a particularly dangerous flaw in email security infrastructure. The crash condition results in immediate service unavailability which can disrupt business operations and create potential denial of service conditions for email services. Organizations using affected ClamAV versions face the risk of having their email systems become unavailable during attack execution, potentially affecting communication workflows and productivity. The vulnerability also creates opportunities for attackers to perform reconnaissance activities by repeatedly triggering crashes to test system resilience.
Mitigation strategies should prioritize immediate patching of ClamAV installations to version 0.89 or later where this vulnerability has been resolved through proper input validation and null pointer checks. Network administrators should implement additional email filtering measures including content inspection and attachment scanning with multiple security layers. The implementation of email quarantining mechanisms can help isolate potentially malicious content before it reaches end users. Security monitoring should be enhanced to detect unusual patterns of service disruption or repeated crash events that may indicate exploitation attempts. Organizations should also consider implementing email encryption and authentication mechanisms to reduce the attack surface. The remediation process should include thorough testing of updated ClamAV versions to ensure that the patch does not introduce compatibility issues with existing email infrastructure. Regular vulnerability assessments and security audits should be conducted to identify similar memory safety issues in other security scanning tools and email filtering systems.