CVE-2018-20436

Severity: high (CVSS 8.1 v3.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.6% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2018-12-24 · updated 2026-06-17
Weakness: CWE-918

Description

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: 4.9.1
Telegram Web: 0.7.0

References

https://misteralfa-hack.blogspot.com/2018/12/abusando-de-telegram-para-conseguir-una.html
https://misteralfa-hack.blogspot.com/2018/12/telegram-siempre-in-middle.html
https://misteralfa-hack.blogspot.com/2018/12/abusando-de-telegram-para-conseguir-una.html
https://misteralfa-hack.blogspot.com/2018/12/telegram-siempre-in-middle.html

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