CVE-2005-3221 in Fortinet Antivirus
Summary
by MITRE
Multiple interpretation error in unspecified versions of Fortinet Antivirus allows remote attackers to bypass virus detection via a malicious executable in a specially crafted RAR file with malformed central and local headers, which can still be opened by products such as Winrar and PowerZip, even though they are rejected as corrupted by Winzip and BitZipper.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 07/30/2017
This vulnerability represents a critical flaw in Fortinet antivirus software's handling of RAR archive files, specifically targeting the archive parsing and virus detection mechanisms. The issue stems from how the antivirus engine interprets the central and local headers within RAR files, creating a scenario where malicious executables can be concealed within archives that appear legitimate to standard archive utilities but are flagged as corrupted by other tools. This discrepancy in interpretation creates a window of opportunity for attackers to bypass security measures through carefully crafted archive structures that exploit the lenient parsing behavior of Fortinet's antivirus solution.
The technical implementation of this vulnerability involves the manipulation of RAR file metadata structures, particularly the central directory header and local file header components that define file attributes, compression methods, and archive organization. Attackers can craft RAR archives where the headers contain contradictory or malformed data that causes different archive utilities to interpret the same file differently. While products like Winrar and PowerZip accept these archives as valid and extract their contents normally, tools such as Winzip and BitZipper reject them as corrupted, demonstrating the inconsistent behavior that enables the bypass mechanism.
The operational impact of this vulnerability extends beyond simple malware delivery, as it represents a fundamental weakness in the antivirus detection methodology that can be exploited across multiple threat vectors. The vulnerability allows attackers to evade security controls by leveraging the differences in archive parsing behavior between various software implementations, potentially enabling the delivery of malicious payloads that would otherwise be detected by traditional antivirus signatures and heuristic analysis. This creates a scenario where a single malicious archive can bypass protection mechanisms across different security solutions, depending on how they handle the malformed archive structures.
This vulnerability aligns with CWE-129, which addresses improper validation of input data, and demonstrates characteristics consistent with ATT&CK technique T1059.007 for execution through command and scripting interpreter, as the bypassed antivirus protection enables malicious code execution. The flaw also relates to CWE-125, which covers out-of-bounds read conditions, as the antivirus engine may attempt to read data beyond properly defined header boundaries. Organizations implementing Fortinet antivirus solutions face significant risk from this vulnerability, as it can be exploited to deliver malware through legitimate archive formats that are commonly used in enterprise environments.
Mitigation strategies should focus on implementing multiple layers of protection beyond signature-based detection, including behavioral analysis, sandboxing, and network-based monitoring to detect anomalous archive extraction patterns. Regular updates to antivirus definitions and firmware should be prioritized, along with implementing network segmentation and content filtering to prevent the delivery of suspicious archive files. Security teams should also consider implementing automated testing procedures to validate archive handling behavior across different software implementations and establish incident response protocols specifically addressing archive-based attack vectors. The vulnerability underscores the importance of comprehensive testing and validation of security solutions against crafted attack scenarios rather than relying solely on standard threat emulation approaches.