Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')

The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes code syntax before inserting the input into an executable resource, such as a library, configuration file, or template.


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

This example attempts to write user messages to a message file and allow users to view them.

$MessageFile = "cwe-94/messages.out";
if ($_GET["action"] == "NewMessage") {
  $name = $_GET["name"];
  $message = $_GET["message"];
  $handle = fopen($MessageFile, "a+");
  fwrite($handle, "<b>$name</b> says '$message'<hr>\n");
  fclose($handle);
  echo "Message Saved!<p>\n";
}
else if ($_GET["action"] == "ViewMessages") {
  include($MessageFile);
}

While the programmer intends for the MessageFile to only include data, an attacker can provide a message such as:

name=h4x0r
message=%3C?php%20system(%22/bin/ls%20-l%22);?%3E

which will decode to the following:

<?php system("/bin/ls -l");?>

The programmer thought they were just including the contents of a regular data file, but PHP parsed it and executed the code. Now, this code is executed any time people view messages.

Notice that XSS (CWE-79) is also possible in this situation.

See Also

Validate Inputs

Weaknesses in this category are related to the design and architecture of a system's input validation components. Frequently these deal with sanitizing, neutralizing a...

Data Neutralization Issues

Weaknesses in this category are related to the creation or neutralization of data using an incorrect format.

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

CWE Cross-section

This view contains a selection of weaknesses that represent the variety of weaknesses that are captured in CWE, at a level of abstraction that is likely to be useful t...


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