CVE-2005-2405 in Web Browser
Summary
by MITRE
Opera 8.01, when the "Arial Unicode MS" font (ARIALUNI.TTF) is installed, does not properly handle extended ASCII characters in the file download dialog box, which allows remote attackers to spoof file extensions and possibly trick users into executing arbitrary code.
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Analysis
by VulDB Data Team • 03/11/2021
This vulnerability exists in Opera 8.01 web browser when the Arial Unicode MS font is installed on the system, creating a specific condition that enables malicious code execution through deceptive file download prompts. The flaw occurs in the browser's handling of extended ASCII characters within the file download dialog box, where the user interface fails to properly sanitize or validate character sequences that could be used to manipulate the visual presentation of file names. The issue stems from improper character encoding handling in the dialog rendering process, specifically when the Arial Unicode MS font is present, which changes how certain extended ASCII characters are displayed and processed.
The technical implementation of this vulnerability involves the manipulation of file extension representations in the download dialog, where attackers can exploit the font rendering behavior to make malicious files appear as legitimate extensions. When the ARIALUNI.TTF font is installed, it affects how certain Unicode and extended ASCII characters are rendered, potentially allowing attackers to insert characters that visually resemble standard file extensions like .exe, .bat, or .scr while maintaining the actual malicious file extension. This creates a spoofing condition where users may be deceived into believing they are downloading benign files when they are actually downloading potentially harmful executables.
The operational impact of this vulnerability extends beyond simple social engineering attacks, as it represents a sophisticated method for bypassing user security awareness training and system defenses. Attackers can leverage this flaw to create convincing deceptive download prompts that exploit the font rendering quirk to hide malicious file types within seemingly legitimate file names, potentially leading to unauthorized code execution on victim systems. The vulnerability specifically targets user trust in the browser's download interface, making it particularly dangerous as it operates at the point of user decision-making for file execution.
This vulnerability aligns with CWE-174, which addresses the weakness of insufficient character encoding handling in user interfaces, and can be mapped to ATT&CK technique T1059 for the execution of malicious code through deceptive file operations. The attack vector requires the victim to have the Arial Unicode MS font installed, which was commonly included with Windows systems, making the exploitation surface quite broad. Security practitioners should note that this represents a classic case of input validation failure in GUI components where the visual presentation of data can be manipulated to deceive users, rather than a traditional code execution vulnerability.
Mitigation strategies should focus on both immediate browser updates and system-level protections. Users should immediately upgrade to newer versions of Opera that address this font handling issue, while system administrators should consider removing or restricting access to the Arial Unicode MS font where it is not essential for legitimate operations. Network-level protections should include enhanced file type validation and content inspection for download prompts, while user education efforts should emphasize the importance of verifying file extensions regardless of visual presentation in download dialogs. Organizations should also implement strict patch management policies to ensure timely updates of browser software and font packages that could introduce similar rendering vulnerabilities.