CVE-2026-109427
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.
Vulnerability class: IDOR (Insecure Direct Object Reference)
Published .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Weakness classification (CWE)
References
- gist.github.com/mansurmavlankulov/489554cad7b38e07b9651c217f00fffb (technical-description)
- www.vulncheck.com/advisories/telegram-stremio-broken-object-authorization-via-s… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-109427?
- CVE-2026-109427 is a medium-severity vulnerability, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 6.5/10. Published 2026-10-12.
- How severe is CVE-2026-109427?
- Medium severity. CVSS v3 base score is 6.5 out of 10.