In this long-read post, we will delve deeper into a serious vulnerability that existed in WhatsApp for Windows prior to version 2.245.6, identified by the code CVE-2025-30401. The vulnerability is a spoofing issue where WhatsApp displayed attachments according to their MIME type, but selected the file opening handler based on the attachment's filename extension, potentially allowing the recipient to inadvertently execute arbitrary code when opening an attachment.

This vulnerability was discovered and responsibly reported by security researchers, leading to the closure of the bug in subsequent updates of the application. In this post, we will discuss the exploit details, provide code snippets for a better understanding of the issue, and provide links to original references so that our readers can further explore this topic.

Exploit Details

WhatsApp for Windows is a popular messaging application used by millions of users worldwide. One of the core features of the application is the ability to send and receive various types of file attachments. When sending an attachment, the sender's client sets the MIME type for the attachment, and the recipient's client decides which program or handler to open the attachment with.

However, in WhatsApp for Windows versions prior to 2.245.6, there was a spoofing issue where the handler chosen by the recipient's client was based on the filename extension, rather than the MIME type. This meant that if an attacker were to send a maliciously crafted mismatched MIME type and filename extension, the recipient could inadvertently execute arbitrary code when they tried to manually open the attachment within the WhatsApp application.

In a real-world attack scenario, the attacker would have to persuade the target to open the attachment, thereby executing the attacker's malicious code. This vulnerability had a high potential to be exploited for social engineering attacks, such as phishing campaigns, where the attacker could impersonate a legitimate contact and send seemingly innocent file attachments that contained hidden malicious code.

Code Snippet

To better understand how this vulnerability could be exploited, let's take a look at a theoretical code snippet demonstrating this mismatch:

// Attacker sends a malicious attachment with mismatched MIME type
// and file extension
{
  "filename": "image.jpg",
  "mime_type": "application/octet-stream",
  "content": "<BASE64_ENCODED_MALICIOUS_CODE>"
}

In this example, the attacker sends a file attachment with an innocent-sounding filename of image.jpg, which would normally be associated with an image file. However, they set the MIME type to application/octet-stream, which could indicate an executable binary file. When the recipient's client receives this attachment, it would display it as an image, but select a handler for opening executable files, potentially running the arbitrary code sent by the attacker when the recipient manually opens the attachment.

Original References / Further Reading
For more information about this vulnerability and its mitigation, including the patch notes and advisory, please refer to the following original sources:

1. NVD - CVE-2025-30401
2. WhatsApp Changelog - version 2.245.6
3. Metasploit Module for CVE-2025-30401 Exploitation

Conclusion

In conclusion, we have explored the details of the CVE-2025-30401 vulnerability, which was a spoofing issue in WhatsApp for Windows that could potentially lead to arbitrary code execution by a recipient who inadvertently opened a maliciously crafted attachment. It is a reminder of the importance of keeping our applications updated with the latest security patches and always being cautious when opening attachments, especially from unknown or unsolicited sources.

Timeline

Published on: 04/05/2025 12:15:14 UTC
Last modified on: 04/07/2025 19:15:56 UTC