LINE, a widely used encrypted messaging app in East Asia, has serious security flaws that could expose users to cyber espionage. Researchers from Aarhus University, Thomas Mogensen and Diego De Freitas Aranha, found vulnerabilities in LINE's custom end-to-end encryption protocol, known as Letter Sealing v2. These flaws allow for message replay attacks, impersonation attacks, and data leakage, impacting millions of users who rely on the app for everyday communications and banking services. The researchers presented their findings, which include the ability for malicious servers to resend encrypted messages at any future time, creating confusion and potentially leading users to disclose sensitive information. LINE’s sticker system and URL previews also expose plaintext data to servers, raising further privacy concerns. Although LINE's parent company, LY Corp., downplayed the risks, asserting that it has implemented measures against man-in-the-middle attacks, the researchers argue that the vulnerabilities stem from the app's inherent design features. Mogensen emphasized the broader implications of these security issues, particularly in corporate and geopolitical contexts. Disgruntled employees or malicious insiders could exploit these vulnerabilities for sabotage or intellectual property theft. The researchers reported that LINE acknowledged the issues but have not committed to significant fixes, leaving users with limited workarounds to enhance their security.