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Methods can return values to communicate failure or success and at other times, or to update the caller's local objects or fields. Security risks can arise if when method return values are simply ignored or if when the invoking method fails to take suitable action. Consequently, programs must not ignore method return values.

When getter methods is not taken on their receipt. Return values may be ignored intentionally or even unintentionally. For example, when getter methods that return a value are named after an action, such as ProcessBuilder.redirectErrorStream(), a programmer may not could fail to realize that a return value is expected. IncidentallyFor example, the only purpose of the ProcessBuilder.redirectErrorStream() method is to tell using a report via return value , whether the process builder merges successfully merged standard error and standard output. The action of actually redirecting method that actually performs redirection of the error stream is performed by its the overloaded single-argument version. It is important to read the API documentation so that return values are not ignoredmethod ProcessBuilder.redirectErrorStream(boolean).

Noncompliant Code Example (File Deletion)

This noncompliant code example attempts to delete a file , but does not fails to check whether the operation has succeeded.:

public void deleteFile(){

  File someFile = new File("someFileName.txt");
  // doDo something with someFile
  someFile.delete();

}

Compliant Solution

This compliant solution checks the (boolean) Boolean value returned by the delete() method and , if necessary, handles the error.handles any resulting errors:

public void deleteFile(){

  File someFile = new File("someFileName.txt");
  // doDo something with someFile
  if (!someFile.delete()) {
    // handleHandle thefailure factto thatdelete the file
 has not been deleted
   }

}

Noncompliant Code Example (String Replacement)

This noncompliant code example ignores the return value of the String.replace() method. As a result, , failing to update the original string is not updated even though it seems otherwise. The String.replace() method does not cannot modify the state of the String but instead, (because String objects are immutable); rather, it returns a reference to a new String object with the replacements in placecontaining the modified string.

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

It is especially important to process the return values of immutable object methods. Although many methods of mutable objects operate by changing some internal state of the object, methods of immutable objects cannot change the object and often return a mutated new object, leaving the original object unchanged.

Compliant Solution

This compliant solution correctly updates the original String object by assigning to it String reference original with the return value from the String.replace() method:

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

Another source of security vulnerabilities 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 can lead to unanticipated unexpected program behavior.

Automated Detection

TODO

Related Vulnerabilities

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

Other Languages

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Related Guidelines

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Bibliography

[API 2006]	method delete() method replace()
[Green 2008]	String.replace
[Pugh 2009]	Misusing putIfAbsent
[Seacord 2015]	Image Added EXP00-J. Do not ignore values returned by methods LiveLesson

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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"

EXP01-J. Ensure a null pointer is not dereferenced      04. Expressions (EXP)      EXP03-J. Do not compare String objects using equality or relational operators