Infinity for Reddit through 8.3.4 contains a login cross-site request forgery vulnerability that allows attackers to log victims into an attacker-controlled account because the exported LoginChromeCustomTabActivity redirect handler checks a hardcoded OAuth state value. Attackers can authorize the app's client ID with their own Reddit account, then deliver an infinity://localhost redirect containing their code and the constant state, causing the victim's posts, messages, and browsing to occur on the attacker's account.