CVE-2024-5692 in Firefox
Summary
by MITRE • 06/11/2024
On Windows, when using the 'Save As' functionality, an attacker could have tricked the browser into saving the file with a disallowed extension such as `.url` by including an invalid character in the extension. *Note:* This issue only affected Windows operating systems. Other operating systems are unaffected. This vulnerability affects Firefox < 127 and Firefox ESR < 115.12.
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Analysis
by VulDB Data Team • 03/24/2025
This vulnerability represents a sophisticated file extension manipulation attack targeting the Windows operating system's file saving mechanisms within web browsers. The flaw exploits a discrepancy in how browsers handle file extensions when users employ the 'Save As' functionality, specifically allowing attackers to bypass normal file extension validation by injecting invalid characters into the extension portion of filenames. The vulnerability is particularly concerning because it leverages operating system-specific behaviors where Windows treats certain file extensions differently than other platforms, creating a unique attack surface that does not exist on non-Windows systems. This type of vulnerability falls under the category of input validation flaws that can lead to arbitrary file creation and potential privilege escalation scenarios.
The technical implementation of this vulnerability stems from how browsers process and sanitize file names during the save operation, particularly when handling special characters or sequences that are normally disallowed in file extensions. When users specify filenames with extensions that contain invalid characters or sequences, the browser's validation logic fails to properly sanitize these inputs, allowing maliciously crafted extensions such as .url to be accepted and saved to disk. The .url extension is particularly dangerous as it represents Windows shortcut files that can contain malicious commands or point to harmful web resources, making this a potential vector for phishing attacks or malware delivery. This vulnerability aligns with CWE-20, which addresses improper input validation, and demonstrates how seemingly benign functionality can become a security risk when input sanitization is inadequate.
The operational impact of this vulnerability extends beyond simple file manipulation and can enable sophisticated attack chains targeting Windows users. Attackers could craft malicious web pages that, when saved by unsuspecting users, create .url files that automatically execute harmful commands or redirect users to malicious sites upon double-clicking. The vulnerability affects both standard Firefox releases and the Extended Support Release versions, indicating a widespread impact across different Firefox deployment scenarios. This creates significant risk for organizations using Firefox as their primary browser, as the attack surface includes not only individual users but also enterprise environments where browser security is critical. The Windows-specific nature of the vulnerability means that while other operating systems remain unaffected, the impact on Windows users is particularly severe due to the platform's native handling of .url files.
Mitigation strategies for this vulnerability should focus on immediate browser updates to versions that address the file extension validation flaw, as well as implementing additional security measures such as restricting file type downloads and educating users about the risks of saving files from untrusted sources. Organizations should also consider implementing browser security policies that restrict the ability to save files with potentially dangerous extensions or that enforce stricter validation of file names. The vulnerability demonstrates the importance of considering platform-specific behaviors when implementing security controls and highlights the need for comprehensive input validation across all browser functionalities. Security teams should monitor for potential exploitation attempts and implement network-based controls to detect and block malicious file downloads that could leverage this vulnerability. This case underscores the critical need for robust file handling validation in web applications and browser environments, particularly when dealing with operating system-specific file system behaviors that could be exploited for privilege escalation or malicious code execution.