Is CVE-2026-109427 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-109427?

CVE-2026-109427 has a CVSS v3 severity of MEDIUM (6.5).

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CVE-2026-109427

Description

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.