Security researchers at ExPatch have uncovered a flaw in Telegram Desktop that allows malicious bots to embed hidden JavaScript in chats, potentially stealing data during HTML exports.

  • A vulnerability exists in Telegram Desktop's HTML export functionality.
  • Malicious bots can plant hidden JavaScript within seemingly normal messages.
  • The exploit triggers when users open exported chat files in a web browser.
  • Data exfiltration can occur silently, stealing entire chat histories.

Security researchers at ExPatch have issued a critical warning regarding a vulnerability discovered in Telegram Desktop. The flaw allows malicious actors to exploit the way users export their chat history into HTML format, potentially leading to massive data breaches.

According to the writeup published on September 12, the attack vector involves a bot sending a message that appears perfectly legitimate to the user. This message often contains a standard-looking link button. However, embedded within the message's structure is a piece of JavaScript code that remains dormant until the user performs a specific action.

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The Mechanics of the Attack

The exploit is triggered when a user utilizes Telegram's built-in feature to export their chat history as an HTML file. When this exported file is subsequently opened in a web browser, the hidden script executes automatically. Once active, the script can scrape every message, contact detail, and piece of sensitive information contained within that HTML file and exfiltrate it to a remote server controlled by the attacker.

This vulnerability highlights a critical gap between real-time messaging security and the security of static data exports.

Why This Matters

BozokMedia analysis shows that this type of attack leverages identity exposure to unlock active attack paths. By mapping cross-domain privilege escalation, attackers can turn a simple chat interaction into a full-scale breach of personal information. This underscores the necessity for platforms to ensure that even offline, exported data remains protected from script injection.

Historical Background

Historically, messaging platforms have struggled with Cross-Site Scripting (XSS) vulnerabilities. While end-to-end encryption protects messages in transit, the moment data is converted into a different format—like an HTML export—it becomes susceptible to traditional web-based vulnerabilities if not properly sanitized.

Did You Know?: JavaScript is the backbone of the modern web, but its ability to run automatically in browsers makes it a primary tool for sophisticated cyberattacks.

Frequently Asked Questions

Question 1: Am I at risk if I use Telegram on my phone?
Answer: This specific flaw is tied to the Telegram Desktop export feature, but staying updated is always recommended.

Question 2: How can I protect my exported data?
Answer: Avoid opening exported HTML files in browsers if you suspect the chat history might contain untrusted content from unknown bots.