CVE-2004-0935 in Sophos
Summary
by MITRE
Eset Anti-Virus before 1.020 (16th September 2004) allows remote attackers to bypass antivirus protection via a compressed file with both local and global headers set to zero, which does not prevent the compressed file from being opened on a target system.
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Analysis
by VulDB Data Team • 01/13/2025
The vulnerability identified as CVE-2004-0935 represents a significant weakness in the Eset Anti-Virus software ecosystem that existed prior to version 1.020 released on September 16, 2004. This security flaw specifically targets the decompression and file analysis mechanisms within the antivirus protection framework, creating a pathway for malicious actors to circumvent security controls through carefully crafted compressed file structures. The vulnerability exploits the software's inability to properly validate compressed file headers, allowing attackers to deliver malicious payloads that would otherwise be detected by standard antivirus scanning mechanisms.
The technical implementation of this vulnerability stems from the way Eset Anti-Virus processes compressed files, particularly those using the zip compression format. When a compressed file contains both local and global headers set to zero, the antivirus software fails to properly recognize the file structure and subsequently does not perform adequate analysis on the contents. This condition creates a false positive scenario where the system believes the file is legitimate or at least not suspicious enough to warrant deeper inspection, allowing potentially malicious code to execute undetected on target systems. The flaw operates at the file parsing level rather than the network level, making it a content-based bypass mechanism that relies on specific header manipulation techniques.
From an operational perspective, this vulnerability presents a substantial risk to organizations relying on Eset Anti-Virus protection, as it allows attackers to bypass security controls without requiring direct exploitation of other system vulnerabilities. The attack vector is particularly concerning because it does not require special privileges or complex attack chains, making it accessible to threat actors with basic knowledge of compressed file structures. Once executed, the malicious payload could potentially lead to full system compromise, data exfiltration, or the establishment of persistent backdoors within the affected environment. This vulnerability specifically aligns with the CWE-129 weakness category, which deals with insufficient validation of the length of input data, and represents a failure in proper input sanitization and validation.
The impact of this vulnerability extends beyond simple bypass capabilities, as it demonstrates a fundamental flaw in how the antivirus software handles edge cases in file processing. Organizations using affected versions of Eset Anti-Virus were essentially operating with a security gap that allowed malicious compressed files to slip through detection mechanisms. The vulnerability's persistence in the software for an extended period before being patched indicates a lack of comprehensive testing for edge cases in file handling routines. This type of vulnerability would typically be categorized under the ATT&CK technique T1059.007 for Command and Scripting Interpreter, as attackers could leverage this bypass to execute malicious code through compressed files, and potentially T1204.002 for User Execution, since the malicious files would need to be opened or executed by users for the attack to succeed.
Mitigation strategies for this vulnerability required immediate patching of Eset Anti-Virus software to version 1.020 or later, which addressed the header validation logic and improved the software's ability to properly analyze compressed files regardless of header values. Organizations should have implemented additional monitoring for unusual compressed file activity and conducted thorough vulnerability assessments to identify any potential exploitation attempts. The remediation process also necessitated updating security policies to include more rigorous testing of compressed file handling capabilities and ensuring that all antivirus software versions were maintained at current patch levels. This vulnerability highlighted the importance of comprehensive testing for edge cases in security software and demonstrated how seemingly minor implementation flaws could create significant security risks in antivirus protection mechanisms.