CVE-2018-5173 in Firefox
Summary
by MITRE
The filename appearing in the "Downloads" panel improperly renders some Unicode characters, allowing for the file name to be spoofed. This can be used to obscure the file extension of potentially executable files from user view in the panel. Note: the dialog to open the file will show the full, correct filename and whether it is executable or not. This vulnerability affects Firefox < 60.
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Analysis
by VulDB Data Team • 03/11/2023
The vulnerability described in CVE-2018-5173 represents a sophisticated user interface rendering issue within the Firefox web browser that exploits Unicode character handling to create deceptive file naming scenarios. This flaw exists specifically within the Downloads panel functionality where the browser fails to properly sanitize or render certain Unicode characters in filenames, creating an opportunity for malicious actors to manipulate how files appear to users. The vulnerability stems from improper Unicode character processing that allows for the concealment of file extensions, particularly when executable file types are disguised with misleading visual representations. This issue affects Firefox versions prior to 60, indicating it was present in a significant portion of the browser's user base during a critical period of web security evolution.
The technical implementation of this vulnerability leverages the browser's handling of Unicode characters within the Downloads panel's filename display mechanism. When processing filenames containing specific Unicode sequences, Firefox fails to properly normalize or sanitize these characters, allowing for the insertion of invisible or visually similar Unicode characters that can alter how filenames appear to end users. This rendering issue creates a scenario where a file named "document.pdf.exe" might be displayed as "document.pdf" in the panel, effectively obscuring the true executable nature of the file. The vulnerability operates at the presentation layer rather than the core file handling mechanism, which means that while the file system and actual file operations remain unaffected, the user interface becomes a vector for deception and social engineering attacks.
The operational impact of this vulnerability extends beyond simple visual deception to create a significant security risk for Firefox users who rely on the Downloads panel for file management and security assessment. Users may be misled into executing potentially malicious files that appear to be benign documents, as the file extension is visually hidden from view. This creates a window of opportunity for phishing attacks, malware distribution, and social engineering campaigns that exploit user trust in familiar file types. The vulnerability's effectiveness is particularly concerning because it operates silently in the background, with the actual file opening dialog correctly displaying the full filename and executable status, meaning users may not realize they have been deceived until after the fact. This characteristic aligns with ATT&CK technique T1059.001 for Windows Command Shell and similar deception patterns that rely on user interface manipulation to bypass security awareness.
The security implications of CVE-2018-5173 demonstrate how seemingly minor UI rendering issues can become significant attack vectors in modern web browsers. This vulnerability represents a classic case of insufficient input validation and sanitization, where Unicode character handling does not adequately account for security implications. The flaw's classification aligns with CWE-180, which addresses incorrect behavior in input processing, and CWE-20, concerning input validation issues. Security researchers have noted that this vulnerability particularly affects user trust models within web browsers, where users implicitly trust the visual representation of files in download panels. The issue highlights the importance of proper Unicode normalization in security-critical interfaces and the potential for internationalization features to introduce unexpected security weaknesses. Organizations and individuals using affected Firefox versions should prioritize immediate patching to prevent exploitation of this vulnerability, as it provides attackers with a straightforward method to bypass user security awareness and potentially deliver malicious payloads through deceptive file naming. The remediation approach involves updating to Firefox 60 or later versions where proper Unicode handling and filename sanitization have been implemented to prevent the spoofing of file extensions in the Downloads panel.