In this post, we will discuss a vulnerability found in Apache Log4j 1.x when used with Chainsaw or SocketAppender components on Java Runtime Environment (JRE) versions less than 1.7, which can lead to a Denial of Service (DoS) attack. It is important to note that this vulnerability only affects products that are no longer receiving support from the maintainer. Upgrading to Apache Log4j 2.x is the recommended solution.

Exploit Details

The vulnerability, identified as CVE-2023-26464, arises from a situation where an attacker manages to create a logging entry that contains a specially-crafted and deeply nested hashmap or hashtable, depending on the logging component in use. When the object is deserialized, it could exhaust the available memory in the Java Virtual Machine (JVM), resulting in a Denial of Service attack.

Here is an example of how such a specially-crafted hashmap could be created

import java.util.HashMap;

public class NestedHashmap {
    public static void main(String[] args) {
        HashMap<String, Object> nestedMap = new HashMap<>();
        HashMap<String, Object> currentLevel = nestedMap;

        for (int i = ; i < 100; i++) {
            HashMap<String, Object> newMap = new HashMap<>();
            currentLevel.put("level_" + i, newMap);
            currentLevel = newMap;
        }

        // Send this object to the vulnerable logging system
    }
}

This code snippet demonstrates how an attacker could create a deeply nested hashmap object that, when processed by the vulnerable logging system, could cause memory exhaustion and ultimately a DoS attack.

Affected Versions

This vulnerability affects Apache Log4j versions prior to 2.x. It should be noted that the vulnerability only affects products that are no longer supported by the maintainer.

Solution

Users of affected Apache Log4j versions should upgrade to Apache Log4j 2.x, which includes a redesigned and more secure logging architecture.

For more information on this vulnerability and the affected Apache Log4j version, you can refer to the following resources:
- Apache Log4j official website: https://logging.apache.org/log4j/1.2/
- Apache Log4j 2.x official website: https://logging.apache.org/log4j/2.x/

Conclusion

In conclusion, CVE-2023-26464 is a vulnerability that affects Apache Log4j 1.x when used with Chainsaw or SocketAppender components on JRE versions less than 1.7. This vulnerability can lead to a Denial of Service attack by causing memory exhaustion in the JVM. Since this vulnerability only affects products that are no longer supported by the maintainer, upgrading to Apache Log4j 2.x is the recommended solution.

Timeline

Published on: 03/10/2023 14:15:00 UTC
Last modified on: 03/15/2023 16:18:00 UTC