CVE-2025-14020 is a user interface (UI) spoofing vulnerability identified in the LINE client for Android versions prior to 14.20. The vulnerability resides in the in-app browser component of the LINE application, specifically in how it handles the display of the full-screen security Toast notification. Normally, this notification serves as a visual security indicator to inform users that they are interacting with a secure or trusted interface. However, when users switch away from the LINE app to another application and then return, the security Toast notification fails to re-display properly. This UI inconsistency can be exploited by attackers to present a spoofed interface that mimics legitimate LINE UI elements or trusted web content within the in-app browser. By leveraging this flaw, attackers can craft phishing attacks that deceive users into divulging sensitive information such as credentials or personal data. The vulnerability has a CVSS v3.1 base score of 5.4, indicating medium severity. It requires no privileges (PR:N) and can be exploited remotely over the network (AV:N), but it does require user interaction (UI:R). The impact primarily affects confidentiality and integrity, with no direct impact on availability. No known exploits have been reported in the wild as of the published date. The vulnerability was publicly disclosed on December 15, 2025, and affects LINE client versions prior to 14.20, including version 10.0. No official patches or mitigation links were provided in the source data, but upgrading to the fixed version is implied.

For European organizations, this vulnerability poses a risk primarily to the confidentiality and integrity of user data accessed through the LINE Android client. Since LINE is widely used for personal and business communication, phishing attacks exploiting this UI spoofing flaw could lead to credential theft, unauthorized access to sensitive conversations, and potential lateral movement within corporate networks if LINE accounts are linked to enterprise resources. The in-app browser is often used to open links without leaving the app, increasing the risk that users may be tricked by spoofed interfaces. Although the vulnerability does not affect availability, the reputational damage and potential data breaches resulting from successful phishing could be significant. Organizations relying on LINE for communication or customer engagement should be aware of this risk, especially in sectors with high regulatory requirements for data protection such as finance, healthcare, and government. The medium severity rating suggests a moderate but actionable threat that should be addressed promptly to prevent exploitation.

1. Upgrade the LINE client for Android to version 14.20 or later as soon as it becomes available, as this version addresses the UI spoofing vulnerability. 2. Educate users about the risks of phishing attacks, emphasizing caution when interacting with links or prompts within the LINE in-app browser, especially after switching between apps. 3. Limit or disable the use of the in-app browser for sensitive transactions or communications where possible, encouraging users to open links in trusted external browsers that have stronger security controls. 4. Implement mobile device management (MDM) policies to enforce app updates and restrict installation of outdated or vulnerable app versions. 5. Monitor network traffic and user reports for suspicious activity related to phishing attempts via LINE messages or links. 6. Encourage multi-factor authentication (MFA) on LINE accounts and any linked services to reduce the impact of credential compromise. 7. Collaborate with LINE Corporation for timely patch releases and security advisories to stay informed about further developments.