CVE-2025-6431 is a security vulnerability identified in Mozilla Firefox for Android versions earlier than 140. The issue arises from the browser's handling of links intended to be opened in external applications. Normally, Firefox for Android prompts users for confirmation before launching an external app to handle a link, serving as a security control to prevent unauthorized or malicious redirections. However, this vulnerability allows an attacker to bypass that prompt, enabling links to open external applications without user consent. This behavior can be exploited by attackers who craft malicious links that, when clicked, trigger actions in external apps without the user's knowledge or approval. The consequence is a potential compromise of application integrity and privacy, as external apps might perform unintended operations or leak sensitive information. The vulnerability is classified under CWE-285 (Improper Authorization), indicating a failure in enforcing proper access control. The CVSS v3.1 base score is 6.5 (medium severity), reflecting that the attack vector is network-based, requires no privileges, but does require user interaction. Confidentiality impact is none, but integrity impact is high, and availability is unaffected. No known exploits have been reported in the wild, and no patches are linked yet, suggesting that mitigation currently relies on user awareness and configuration adjustments. This vulnerability is specific to Firefox for Android and does not affect desktop or other mobile versions of Firefox.

For European organizations, the primary impact of CVE-2025-6431 lies in the potential compromise of mobile device security and user privacy. Many enterprises rely on Firefox for Android as a secure browser for mobile workforce productivity. The bypass of the external app prompt could allow attackers to execute unauthorized actions in other installed applications, such as messaging apps, email clients, or productivity tools, potentially leading to data integrity issues or leakage of sensitive information. This could facilitate targeted phishing or social engineering attacks, where malicious links trigger unintended behaviors without user consent. The impact is heightened in sectors with strict data protection requirements, such as finance, healthcare, and government, where privacy leaks or unauthorized data manipulation could have regulatory and reputational consequences. Although no availability impact is expected, the integrity compromise could undermine trust in mobile device security. The lack of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits once patches are released. Organizations with a significant number of Android users who use Firefox should consider this vulnerability in their mobile security posture.

1. Monitor Mozilla’s official channels for the release of security patches addressing CVE-2025-6431 and apply updates to Firefox for Android promptly once available. 2. Until patches are released, consider configuring Firefox for Android to restrict or disable opening links in external applications where feasible, reducing the attack surface. 3. Educate users about the risks of clicking unsolicited or suspicious links, especially on mobile devices, to mitigate social engineering vectors. 4. Employ mobile device management (MDM) solutions to enforce security policies that limit app interactions or control which external applications can be invoked from browsers. 5. Implement network-level protections such as URL filtering and threat intelligence to block access to known malicious sites that could exploit this vulnerability. 6. Conduct regular security awareness training focusing on mobile security hygiene and phishing prevention. 7. Review and audit installed external applications on corporate devices to ensure they do not have excessive permissions that could be abused if triggered maliciously. 8. Consider deploying endpoint detection and response (EDR) solutions capable of monitoring unusual app launches or behaviors on mobile devices.