CVE-2021-36214 in LINE
Summary
by MITRE • 07/13/2021
LINE client for iOS before 10.16.3 allows cross site script with specific header in WebView.
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Analysis
by VulDB Data Team • 04/09/2026
The vulnerability identified as CVE-2021-36214 affects the LINE client application for iOS operating systems prior to version 10.16.3. This represents a significant security flaw that manifests through improper input validation within the application's web view component, specifically when processing certain HTTP headers. The issue stems from the application's failure to adequately sanitize or validate header data before rendering content within its embedded WebView, creating an environment where malicious actors can potentially exploit this weakness to execute unauthorized code.
The technical flaw resides in the WebView implementation within the LINE iOS application, where specific HTTP headers containing malicious script content are not properly filtered or escaped before being processed by the web rendering engine. This vulnerability falls under the category of cross-site scripting attacks and aligns with CWE-79 which describes improper neutralization of input during web page generation. The vulnerability occurs because the application's WebView component does not implement adequate security measures to prevent script injection attacks, particularly when dealing with headers that may contain user-controllable data. Attackers can craft malicious HTTP responses or manipulate headers in a way that causes the WebView to execute unintended JavaScript code when processing content.
The operational impact of this vulnerability is substantial as it allows attackers to potentially execute arbitrary code within the context of the LINE application's WebView. This could enable various malicious activities including but not limited to credential theft, session hijacking, data exfiltration, or redirection to malicious websites. The attack surface is particularly concerning given that LINE is a widely used messaging application with millions of users globally, making successful exploitation potentially scalable across a large user base. The vulnerability specifically targets iOS users, which may provide attackers with access to sensitive communication data, personal information, and potentially device-level access depending on the execution context.
Security professionals should note that this vulnerability demonstrates poor input validation practices within mobile applications and highlights the importance of implementing proper sanitization mechanisms for all user-controllable data. The issue is particularly relevant in the context of the ATT&CK framework where it could map to techniques such as T1059.007 for script execution and T1566 for social engineering attacks that leverage mobile applications. Organizations should implement immediate mitigations including updating to LINE client version 10.16.3 or later, which contains the necessary patches to address the header validation issues. Additionally, network administrators should monitor for suspicious traffic patterns and consider implementing additional security controls such as web application firewalls or content filtering mechanisms to detect and prevent exploitation attempts. The vulnerability underscores the critical need for mobile application security testing and proper secure coding practices, particularly when handling web content within native applications.