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Methods return values to signify failure or success or, at other times, to update the caller's objects or fields. Security risks can arise if return values are simply ignored or if suitable action is not taken on their receipt.

Noncompliant Code Example

This noncompliant code example attempts to delete a file, but does not check that the operation succeeds.

  File someFile = new File("someFileName.txt");

  // do something with someFile

  someFile.delete();

Compliant Solution

In the compliant solution, the (boolean) value returned by the delete() method is checked and, if necessary, the error is handled.

  File someFile = new File("someFileName.txt");

  // do something with someFile

  if (!someFile.delete()) {
    // handle the fact that the file has not been deleted
  }

Noncompliant Code Example

This noncompliant code example ignores the return value while making use of the String.replace method. As a result, the original string is not updated even though it seems otherwise. The String.replace() method does not modify the state of the String but instead, returns a reference to a new String object with the replacements in effect.

public class Ignore {
  public static void main(String[] args) {
    String original = "insecure";
    original.replace( 'i', '9' );
    System.out.println(original);
  }
}

Compliant Solution

The compliant solution correctly updates the original string object by assigning to it the return value.

public class DoNotIgnore {
  public static void main(String[] args) {
    String original = "insecure";
    original = original.replace( 'i', '9' );
    System.out.println(original);
  }
}

Another source of coding bugs caused by ignoring return values is detailed in FIO02-J. Keep track of bytes read and account for character encoding while reading data.

Risk Assessment

Ignoring method return values may lead to erroneous computation which, in turn, may lead to vulnerabilities.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Other Languages

This rule appears in the C Secure Coding Standard as EXP12-C. Do not ignore values returned by functions.

This rule appears in the C++ Secure Coding Standard as EXP12-CPP. Do not ignore values returned by functions or methods.

References

\[[API 06|AA. Java References#API 06]\] method [delete()|http://java.sun.com/javase/6/docs/api/java/io/File.html#delete()]
\[[API 06|AA. Java References#API 06]\] method [replace()|http://java.sun.com/javase/6/docs/api/java/lang/String.html#replace(char,%20char)]
\[[Green 08|AA. Java References#Green 08]\] ["String.replace"|http://mindprod.com/jgloss/gotchas.html]
\[[Pugh 09|AA. Java References#Pugh 09]\] misusing putIfAbsent
\[[MITRE 09|AA. Java References#MITRE 09]\] [CWE ID 252|http://cwe.mitre.org/data/definitions/252.html] "Unchecked Return Value"

EXP00-J. Use the same type for the second and third operands in conditional expressions      03. Expressions (EXP)      EXP03-J. Do not compare String objects using equality or relational operators