CVE-2026-109427

10th percentile - higher than 10% of all known CVEs

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.

An organization using Telegram-Stremio may experience leakage of private messages, channels, and groups, including the operator's Saved Messages. This can lead to a breach of communication confidentiality and exposure of sensitive business or personal information.

Upgrade Telegram-Stremio to a version later than 5.1.0 if available, or implement additional validation of tokens and stream IDs. Restrict access to the stream_handler and thumb_handler endpoints and monitor for unusual chat access requests.