CVE-2025-6426 is a high-severity vulnerability affecting Mozilla Firefox on macOS platforms, specifically versions prior to Firefox 140 and Firefox ESR prior to 128.12, as well as Thunderbird versions before 140 and 128.12 respectively. The vulnerability arises because Firefox on macOS fails to display a warning prompt when users attempt to open executable files with the '.terminal' extension. Normally, browsers warn users before opening potentially executable files to prevent inadvertent execution of malicious code. However, due to this flaw, users may unknowingly execute terminal scripts or commands, which can lead to arbitrary code execution. This vulnerability is classified under CWE-345, indicating insufficient verification of data authenticity or integrity. The CVSS v3.1 base score is 8.8, reflecting its high impact and relatively low complexity of exploitation. The attack vector is network-based (AV:N), requiring no privileges (PR:N), but user interaction is necessary (UI:R). The vulnerability impacts confidentiality, integrity, and availability (C:H/I:H/A:H), meaning an attacker could fully compromise the affected system by tricking a user into opening a malicious '.terminal' file via Firefox on macOS. No known exploits are currently reported in the wild, but the potential for exploitation remains significant given the ease of triggering the vulnerability through user interaction. This issue is limited to macOS Firefox and Thunderbird clients, with other platforms unaffected. No patch links were provided at the time of reporting, indicating that users should monitor Mozilla advisories for updates.

For European organizations, this vulnerability poses a substantial risk, especially those with macOS users who rely on Firefox or Thunderbird for web browsing and email communication. Successful exploitation could lead to arbitrary code execution, enabling attackers to install malware, steal sensitive information, disrupt services, or gain persistent access to corporate networks. Given the high confidentiality, integrity, and availability impacts, critical infrastructure, financial institutions, government agencies, and enterprises handling sensitive data are at heightened risk. The requirement for user interaction means phishing or social engineering campaigns could be leveraged to exploit this vulnerability. Since macOS adoption is significant in sectors such as creative industries, technology firms, and academia across Europe, the threat surface is non-trivial. Additionally, the lack of warning when opening executable terminal files increases the likelihood of accidental compromise by less security-aware users. The absence of known exploits in the wild currently provides a window for proactive mitigation, but organizations should act swiftly to reduce exposure.

European organizations should implement targeted measures beyond generic advice: 1) Enforce strict endpoint security policies that restrict or monitor execution of '.terminal' files on macOS devices. 2) Deploy advanced email and web filtering solutions to detect and block suspicious attachments or downloads with '.terminal' extensions. 3) Conduct focused user awareness training emphasizing the risks of opening unknown executable files, particularly those with terminal extensions, and recognizing phishing attempts. 4) Utilize macOS security features such as Gatekeeper and System Integrity Protection (SIP) to limit unauthorized code execution. 5) Monitor Mozilla security advisories closely and prioritize patching Firefox and Thunderbird to versions 140/128.12 or later as soon as updates become available. 6) Implement application whitelisting or endpoint detection and response (EDR) tools capable of detecting anomalous execution behaviors related to terminal scripts. 7) Consider temporarily restricting the use of Firefox and Thunderbird on macOS in highly sensitive environments until patches are applied. These steps, combined with robust incident response readiness, will help mitigate the risk posed by this vulnerability.