CVE-2026-109427

Telegram-Stremio through 5.1.0 contains a broken object-level authorization vulnerability that allows authenticated token holders to access arbitrary chat messages by forging unsigned, unauthenticated stream IDs decoded via encode string/decode string functions. Attackers can craft or enumerate sequential msg id values and set a global flag in the stream handler endpoint to route requests through the operator's personal Userbot account, exposing private channels, groups, and Saved Messages, while the unauthenticated thumb handler endpoint further discloses thumbnails from those same chats without any token validation.