CVE-2024-47535: Netty Denial of Service Vulnerability through Unsafe Environment File Reading

Netty is a popular asynchronous event-driven network application framework that allows developers to build high-performance protocol servers and clients with ease and maintainability. However, a recent vulnerability has been discovered in Netty, which could result in a denial of service attack.

This blog post will provide an in-depth analysis of CVE-2024-47535, its potential impact on applications using the Netty framework, and how to mitigate the vulnerability to ensure your applications remain secure. We'll also include code snippets and links to original references for further information.

CVE-2024-47535: Vulnerability Details

CVE-2024-47535 is a security vulnerability caused by an unsafe reading of an environment file in the Netty framework. Specifically, when a Windows application running on Netty tries to load a file that does not exist, it could result in the application crashing, and thus, causing a denial of service attack.

An attacker, by creating an extremely large file, could potentially exploit this vulnerability to crash the Netty application, rendering it unavailable. The vulnerability has been patched in Netty version 4.1.115.

Here's a code snippet that demonstrates the unsafe environment file reading in Netty

Path envFile = Paths.get(System.getenv("NETTY_ENV_FILE"));
try (Stream<String> lines = Files.lines(envFile)) {
    lines.forEach(line -> {
        // Process each line from the environment file
    });
} catch (IOException e) {
    // Log or handle the exception caused by reading a non-existing or large file
}

The unsafe reading happens when Netty tries to read the environment file without checking if the file exists. Moreover, this code does not handle cases when the file is abnormally large, as created by a malicious attacker.

Original Reference - Vulnerability Disclosure

The vulnerability was originally disclosed and discussed in this GitHub issue: Unsafe reading of environment file in Netty

In this issue, it was discovered that the unsafe file reading could cause a denial of service in Netty applications.

Exploit Details and Mitigation Steps

To exploit CVE-2024-47535, an attacker would need to create a large file as specified in System.getenv("NETTY_ENV_FILE") and ensure that a Netty application on Windows attempts to read the file, possibly causing a denial of service.

To mitigate this vulnerability, ensure that the Netty framework you use is updated to version 4.1.115 or higher. Additionally, make sure to validate the environment file before reading it, by both checking if it exists and ensuring that it's within an acceptable size limit.

Here's how you can implement a safer file reading in your application

Path envFile = Paths.get(System.getenv("NETTY_ENV_FILE"));
if (Files.exists(envFile) && Files.size(envFile) < MAXIMUM_SIZE_LIMIT) {
    try (Stream<String> lines = Files.lines(envFile)) {
        lines.forEach(line -> {
            // Process each line from the environment file
        });
    } catch (IOException e) {
        // Log or handle the exception caused by reading the file
    }
} else {
    // Log or handle the non-existence or abnormal size of the environment file
}

In this revised code snippet, we check if the file exists and if it's within an acceptable size limit before attempting to read its contents.

Conclusion

CVE-2024-47535 is a security vulnerability in the Netty framework that could potentially result in a denial of service attack. Ensure your applications using the Netty framework are updated to version 4.1.115 or later, and take necessary precautions in safely reading environment files. By following the recommended mitigation steps, you can protect your applications from this vulnerability and ensure they remain secure.

Timeline

Published on: 11/12/2024 16:15:22 UTC
Last modified on: 11/13/2024 17:01:58 UTC