WhatsApp Retransmission Exploit: Attack Guide

TL;DR

This guide details how an attacker could exploit WhatsApp’s retransmission vulnerability to deliver malicious payloads or intercept communications. The attack relies on manipulating message delivery and exploiting the application’s handling of failed transmissions.

Understanding the Vulnerability

WhatsApp, like many messaging apps, uses a system for reliably delivering messages. If a message fails to send initially, it will be retransmitted. The vulnerability occurs when WhatsApp doesn’t properly validate or sanitise data during these retransmission attempts. This can allow an attacker to inject malicious content into the retransmission process.

Attack Steps

1. Prerequisites: You’ll need a target WhatsApp account and the ability to send them messages. Tools like Wireshark or tshark are helpful for network analysis, but not strictly required initially.
2. Initial Message Send: Send a seemingly harmless message to the target. This establishes a communication channel and triggers the retransmission mechanism when intentionally disrupted.
3. Network Interruption (Simulate Failed Delivery): Interrupt the network connection *immediately* after sending the initial message. This can be done by:
   • Temporarily disabling Wi-Fi or mobile data on your device.
   • Using a network firewall to block WhatsApp’s traffic (ports 443 and 5228 are common). For example, using `iptables` on Linux:

     sudo iptables -A OUTPUT -p tcp --dport 443 -j DROP

   • Using a man-in-the-middle (MITM) proxy to delay or drop packets.
4. Malicious Payload Injection: While the connection is interrupted, craft a malicious message designed to exploit the retransmission process. This payload could take several forms:
   • Cross-Site Scripting (XSS): Inject JavaScript code into the message content. If WhatsApp doesn’t properly sanitise this during retransmission, it could execute in the target’s browser when viewing the message link.
   • Phishing Links: Include a link to a malicious website designed to steal credentials or install malware.
   • Exploitable Media Files: Send an image or video file containing embedded exploits (e.g., crafted EXIF data).
5. Restore Network Connection: Re-enable the network connection. WhatsApp will attempt to retransmit the message, now including your injected payload.
6. Payload Delivery & Execution: If successful, the malicious payload will be delivered to the target’s device and potentially executed.
   • For XSS, the target needs to click a link within the message.
   • For phishing links, the target must visit the malicious website.
   • For media files, execution depends on how WhatsApp handles the file type (e.g., opening in an image viewer).
7. Monitoring & Analysis: Use network analysis tools like Wireshark to confirm that the malicious payload was transmitted and received by the target’s device. Look for unusual traffic patterns or suspicious data within the WhatsApp communication stream.

   tshark -i  whatsapp

Important Considerations

• WhatsApp Security Measures: WhatsApp implements various security measures to prevent these types of attacks, including end-to-end encryption and input validation. This attack is more likely to succeed against older versions of WhatsApp or in scenarios where the target’s device has been compromised.
• Ethical Hacking: This information is provided for educational purposes only. Attempting to exploit this vulnerability without explicit permission is illegal and unethical.
• Rate Limiting: WhatsApp may implement rate limiting to prevent excessive retransmission attempts, making the attack more difficult.

Mitigation

• Keep WhatsApp Updated: Regularly update WhatsApp to benefit from the latest security patches.
• Be Cautious of Links and Files: Avoid clicking on suspicious links or opening files from unknown sources.
• Enable Two-Step Verification: Add an extra layer of security to your account by enabling two-step verification.