The issue concerns a side channel in the "secret chat" feature where Telegram servers send GET requests for URLs typed while composing a chat message, before the message is sent. Additionally, GET requests are sent to other URLs on the same web server. This can also be interpreted as a Server-Side Request Forgery (SSRF) issue. A third party has reported that the behavior may be caused by misconfiguration of the "Secret chats > Preview links" setting.