CVE-2025-6431 in Firefox
Summary
by MITRE • 06/24/2025
When a link can be opened in an external application, Firefox for Android will, by default, prompt the user before doing so. An attacker could have bypassed this prompt, potentially exposing the user to security vulnerabilities or privacy leaks in external applications. *This bug only affects Firefox for Android. Other versions of Firefox are unaffected.* This vulnerability affects Firefox < 140.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/17/2025
This vulnerability represents a critical security flaw in Firefox for Android that undermines the browser's default security mechanisms designed to protect users from potentially malicious external application launches. The issue stems from a bypassable user prompt that is normally intended to warn users before opening links in external applications, creating a pathway for attackers to circumvent these protective measures without user awareness or consent. The vulnerability specifically affects Firefox for Android versions prior to 140, leaving users of these older versions exposed to potential security risks and privacy violations. This represents a significant regression in the browser's security posture that could enable various attack vectors including phishing attempts, malicious application exploitation, and unauthorized data access through external application interfaces.
The technical implementation flaw involves the bypass mechanism that allows attackers to skip the user confirmation prompt that should normally appear when attempting to open links in external applications. This bypass occurs at the application launch handling level within Firefox for Android's security architecture, where the normal flow of user consent is disrupted. The vulnerability is classified as a privilege escalation or user consent bypass issue that enables attackers to perform actions that users would normally be prompted to approve. According to CWE standards, this vulnerability aligns with CWE-693, which covers protection mechanism failures, and CWE-352, which addresses cross-site request forgery. The flaw essentially removes the user's ability to make informed decisions about external application access, which is a fundamental security principle in mobile application design and user interface security.
The operational impact of this vulnerability extends beyond simple privacy concerns to encompass potential data breaches, malicious software installation, and unauthorized access to user information through external applications. Attackers could exploit this flaw to redirect users to malicious applications without their knowledge, potentially leading to credential theft, device compromise, or data exfiltration. The vulnerability particularly affects users who frequently interact with web content that links to external applications, such as banking applications, social media platforms, or file sharing services. Mobile security frameworks and threat models like those defined in the ATT&CK framework would classify this as a user interface deception technique, specifically related to privilege escalation and application control bypass. The attack surface includes scenarios where users might be tricked into opening malicious external applications through social engineering or compromised websites, with the attacker leveraging the bypass to execute malicious payloads without user awareness.
Organizations and users should immediately upgrade to Firefox version 140 or later to remediate this vulnerability, as no effective workarounds exist for the bypass mechanism. System administrators should monitor for affected devices and implement mobile device management policies to ensure timely updates. The vulnerability highlights the importance of maintaining current browser versions and implementing proper security controls for mobile environments. Security teams should conduct vulnerability assessments to identify affected devices and implement network monitoring to detect potential exploitation attempts. Additional mitigations include educating users about the risks of clicking external links and implementing browser security policies that enforce secure application handling practices. The vulnerability also underscores the need for comprehensive mobile browser security testing and the importance of maintaining robust user consent mechanisms in mobile application environments.