CVE-2018-20436: Telegram

High severity, CVSS 8.1. EPSS: 1.6% chance of exploitation in the next 30 days.

The "secret chat" feature in Telegram 4.9.1 for Android has a "side channel" in which Telegram servers send GET requests for URLs typed while composing a chat message, before that chat message is sent. There are also GET requests to other URLs on the same web server. This also affects one or more other Telegram products, such as Telegram Web-version 0.7.0. In addition, it can be interpreted as an SSRF issue. NOTE: a third party has reported that potentially unwanted behavior is caused by misconfiguration of the "Secret chats > Preview links" setting

Affected products

• Telegram Telegram: version 4.9.1 only
• Telegram Web: version 0.7.0 only

Published 2018-12-24. Last modified 2026-06-17.