A deep link validation issue in KakaoTalk 10.4.3 allowed a remote adversary to direct users to run any attacker-controlled JavaScript within a WebView. The impact was further escalated by triggering another WebView that leaked its access token in a HTTP request header. Ultimately, this access token could be used to take over another user's account and read her/his chat messages.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.