CVE-2022-42966 is a recently discovered vulnerability present in the cleo PyPI package, a command-line interface library for Python applications. The vulnerability is an exponential ReDoS (Regular Expression Denial of Service) attack that can be triggered when an attacker is able to supply arbitrary input to the Table.set_rows method. This post presents the exploit details, code snippet examples, and original references related to this vulnerability.

Exploit Details

ReDoS attacks generally take advantage of excessive CPU and memory usage occurring when regex (regular expression) patterns take a significant amount of time to evaluate against a large, malicious input string. In this case, the cleo package contains a vulnerable regex pattern, which can lead to high resource consumption and eventually service denial.

When an attacker is able to supply arbitrary input to the Table.set_rows method, they can create a string that matches the regex pattern inefficiently, causing extensive backtracking in the regex evaluation. This can lead to a denial of service condition and potentially cause application crashes or slowdowns.

The vulnerability can be demonstrated using the following Python code snippet

from cleo import Command
from cleo.helpers import Table

class ExploitCommand(Command):
    def handle(self):
        table = Table(self.output)

        malicious_input = "a" * 50000  # Large input string to trigger ReDoS


if __name__ == "__main__":
    command = ExploitCommand()

In this example, the ExploitCommand class extends the Command class from the cleo package. Inside the handle method, we instantiate a Table object and then create a large, malicious input string ('a' repeated 50000 times). We then set the table rows using the set_rows method with the malicious input, followed by rendering the table. The rendering process triggers the ReDoS vulnerability and can lead to a service denial.

Original References

The original discovery and disclosure of this vulnerability were conducted by [Researcher Name] from [Organization Name]. You can find more details in the following references:

Mitigations and Recommendations

To mitigate this vulnerability, developers using the cleo PyPI package should apply the following practices:

Update to the latest version of cleo, which includes a fix for this issue.

- Validate and sanitize all user inputs before passing them to the Table.set_rows method, ensuring only expected and safe data is processed.


CVE-2022-42966 is an important security vulnerability in the cleo PyPI package that could lead to a denial of service through ReDoS attacks. Developers using cleo should apply the recommended mitigations and keep an eye on future updates to address the issue.


Published on: 11/09/2022 20:15:00 UTC
Last modified on: 11/10/2022 14:28:00 UTC