CVE-2020-6797 in Firefox
Summary
by MITRE
By downloading a file with the .fileloc extension, a semi-privileged extension could launch an arbitrary application on the user's computer. The attacker is restricted as they are unable to download non-quarantined files or supply command line arguments to the application, limiting the impact. Note: this issue only occurs on Mac OSX. Other operating systems are unaffected. This vulnerability affects Thunderbird < 68.5, Firefox < 73, and Firefox < ESR68.5.
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Analysis
by VulDB Data Team • 05/11/2025
This vulnerability represents a significant security flaw in Mozilla's Firefox and Thunderbird applications on macOS platforms, specifically related to how the browser handles file associations and extension processing. The issue stems from improper handling of the .fileloc extension which allows malicious actors to potentially execute arbitrary applications through crafted file downloads. The vulnerability is classified as a privilege escalation vector that could be exploited by semi-privileged extensions, meaning that attackers with limited access rights could leverage this flaw to gain broader system control. The technical implementation involves the browser's file association system failing to properly validate or sanitize file types associated with the .fileloc extension, creating a pathway for unauthorized application execution. This represents a clear violation of the principle of least privilege and demonstrates a failure in the application's security model for handling user-initiated file operations.
The operational impact of this vulnerability is substantial within the targeted macOS environment, as it enables attackers to execute arbitrary applications without user consent or awareness. While the attack vector is somewhat constrained - attackers cannot download non-quarantined files or pass command line arguments to applications - the core threat remains significant because the flaw allows for automatic application launching through seemingly benign file downloads. The vulnerability affects multiple versions of Firefox and Thunderbird, specifically those below 68.5 for Thunderbird and 73 for Firefox, as well as ESR68.5, indicating this was a widespread issue affecting the browser ecosystem. The macOS-specific nature of the flaw means that users of other operating systems remain unaffected, but for Mac users, the implications are severe as it could enable various attack scenarios including malware installation, system reconnaissance, or privilege escalation attacks. This vulnerability aligns with CWE-78, which addresses improper neutralization of special elements in OS commands, and represents a classic example of how file association handling can create dangerous execution paths.
The security implications extend beyond simple application execution, as this vulnerability could serve as a launching point for more sophisticated attacks within the macOS environment. Attackers could potentially use this flaw to execute malicious applications that would otherwise be blocked by macOS security mechanisms, effectively bypassing Gatekeeper and other system protections. The restriction on downloading non-quarantined files and supplying command line arguments suggests that the vulnerability's design limits its scope, but still provides attackers with sufficient capability to compromise user systems. This flaw demonstrates the importance of proper input validation and file type handling in browser applications, particularly in environments where system-level privileges and user security are paramount. The vulnerability's classification under the ATT&CK framework would likely fall under T1059 for command and scripting interpreter execution, with potential lateral movement implications through the execution of malicious applications. Organizations using these affected browser versions should immediately implement mitigations including version updates, browser hardening measures, and user education about the risks of downloading unknown files with unusual extensions. The remediation approach should focus on updating to patched versions of Firefox and Thunderbird while implementing additional controls such as extension whitelisting and enhanced file type validation to prevent similar issues from occurring in the future.