Improper Output Neutralization for Logs

Description

Background

Applications typically use log files to store a history of events or transactions for later review, statistics gathering, or debugging. Depending on the nature of the application, the task of reviewing log files may be performed manually on an as-needed basis or automated with a tool that automatically culls logs for important events or trending information.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following web application code attempts to read an integer value from a request object. If the parseInt call fails, then the input is logged with an error message indicating what happened.

String val = request.getParameter("val");
try {


  int value = Integer.parseInt(val);

}
catch (NumberFormatException) {
  log.info("Failed to parse val = " + val);
}
...

If a user submits the string "twenty-one" for val, the following entry is logged:

However, if an attacker submits the string "twenty-one%0a%0aINFO:+User+logged+out%3dbadguy", the following entry is logged:

Clearly, attackers can use this same mechanism to insert arbitrary log entries.

See Also