CVE-2025-1939 is a security vulnerability identified in Mozilla Firefox versions prior to 136, specifically affecting the Android implementation of Custom Tabs. Custom Tabs allow Android applications to load web content within the app context while leveraging the browser's rendering engine, providing a seamless user experience. This vulnerability arises from the use of transition animations within Custom Tabs, which can be exploited for tapjacking attacks. Tapjacking is a technique where an attacker overlays or manipulates UI elements to trick users into interacting with hidden or disguised interface components, potentially causing them to grant sensitive permissions or perform unintended actions. In this case, the transition animations could be used to obscure what the user is actually clicking, misleading them into authorizing permissions or actions they did not intend. The vulnerability is classified under CWE-359 (Exposure of Sensitive Information Through UI Elements), indicating that the UI manipulation leads to exposure or misuse of sensitive information or permissions. The CVSS v3.1 base score is 3.9, indicating a low severity level. The vector indicates that the attack requires local access (AV:L), low attack complexity (AC:L), privileges (PR:L), and user interaction (UI:R). The impact affects confidentiality and integrity to a limited extent, with no impact on availability. There are no known exploits in the wild at the time of publication, and no patch links have been provided yet. This suggests that the vulnerability is newly discovered and may be addressed in upcoming Firefox updates.

For European organizations, the impact of this vulnerability is relatively limited but still notable. Since it involves Android Custom Tabs within Firefox, the threat primarily targets mobile users who access web content through apps leveraging this feature. Potential impacts include unauthorized granting of sensitive permissions (such as access to location, camera, microphone, or contacts) due to deceptive UI overlays, which could lead to data leakage or privacy violations. Organizations with employees or customers using Firefox on Android devices are at risk of social engineering attacks exploiting this vulnerability. While the severity is low, targeted attacks could leverage this to gain footholds or escalate privileges within mobile environments. Privacy-sensitive sectors such as finance, healthcare, and government entities in Europe could be more concerned due to the potential exposure of sensitive user data. However, the requirement for local access and user interaction reduces the likelihood of widespread automated exploitation. The absence of known exploits suggests that the threat is not yet actively leveraged by attackers, providing a window for mitigation.

To mitigate this vulnerability, European organizations should prioritize updating Mozilla Firefox to version 136 or later once the patch is released. Until then, organizations can implement the following practical measures: 1) Educate users about the risks of tapjacking and encourage vigilance when granting permissions on mobile devices, especially when prompted unexpectedly. 2) Restrict installation of untrusted or unnecessary Android applications that might embed malicious Custom Tabs. 3) Employ mobile device management (MDM) solutions to enforce security policies that limit app permissions and monitor suspicious app behaviors. 4) Encourage the use of alternative browsers or disable Custom Tabs usage in critical environments if feasible. 5) Monitor Firefox security advisories and apply patches promptly to reduce exposure time. 6) For developers, review app implementations that use Custom Tabs to ensure they do not inadvertently enable or expose transition animations that could be exploited. These steps go beyond generic advice by focusing on user education, app management, and proactive patching tailored to this specific vulnerability.