Methods can return values to communicate failure or success or to update local objects or fields. Security risks can arise when method return values are ignored or when the invoking method fails to take suitable action. When getter methods are named after an action, a programmer might fail to realize that a return value is expected. For example, the only purpose of the {{ProcessBuilder.redirectErrorStream()}} method is to report via return value whether the process builder successfully merges standard error and standard output. The method that actually performs redirection of the error stream is the overloaded single-argument version.
{mc}
Another example is ignoring the return value from add() on a HashSet. If duplicate, false will be returned.
{mc}
h2. Noncompliant Code Example (File Deletion)
This noncompliant code example attempts to delete a file, but fails to check whether the operation has succeeded.
{code:bgColor=#FFcccc}
File someFile = new File("someFileName.txt");
// do something with someFile
someFile.delete();
{code}
h2. Compliant Solution
This compliant solution checks the ({{boolean}}) value returned by the {{delete()}} method and handles any resulting errors.
{code:bgColor=#ccccff}
File someFile = new File("someFileName.txt");
// do something with someFile
if (!someFile.delete()) {
// handle failure to delete the file
}
{code}
h2. Noncompliant Code Example (String Replacement)
This noncompliant code example ignores the return value of the {{String.replace()}} method, failing to update the original string. The {{String.replace()}} method cannot modify the state of the {{String}} (because {{String}} objects are immutable); rather, it returns a reference to a new {{String}} object containing the desired result.
{code:bgColor=#FFcccc}
public class Ignore {
public static void main(String[] args) {
String original = "insecure";
original.replace( 'i', '9' );
System.out.println(original);
}
}
{code}
It is especially important not to ignore the return values of immutable object methods. While many methods of mutable objects operate by changing some internal state of the object, methods of immutable objects can't change the object and often will return a new object with some mutation, leaving the original object unchanged.
h2. Compliant Solution
This compliant solution correctly updates the {{String}} reference {{original}} with the return value from the {{String.replace()}} method.
{code:bgColor=#ccccff}
public class DoNotIgnore {
public static void main(String[] args) {
String original = "insecure";
original = original.replace( 'i', '9' );
System.out.println(original);
}
}
{code}
h2. Risk Assessment
Ignoring method return values can lead to unexpected program behavior.
|| Guideline || Severity || Likelihood || Remediation Cost || Priority || Level ||
| EXP00-J | medium | probable | medium | {color:#cc9900}{*}P8{*}{color} | {color:#cc9900}{*}L2{*}{color} |
h3. Automated Detection
The Coverity Prevent Version 5.0 *CHECKED_RETURN* checker can detect the instance where Value returned from a function is not checked for errors before being used.
h3. Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this guideline on the [CERT website|https://www.kb.cert.org/vulnotes/bymetric?searchview&query=FIELD+KEYWORDS+contains+EXP02-J].
h2. Related Guidelines
C Secure Coding Standard: [seccode:EXP12-C. Do not ignore values returned by functions]
C+\+ Secure Coding Standard: [cplusplus:EXP12-CPP. Do not ignore values returned by functions or methods]
h2. Related Guidelines
[MITRE CWE|http://cwe.mitre.org/]: [CWE-252|http://cwe.mitre.org/data/definitions/252.html] "Unchecked Return Value"
h2. Bibliography
\[[API 2006|AA. Bibliography#API 06]\] method [delete()|http://java.sun.com/javase/6/docs/api/java/io/File.html#delete()] and method [replace()|http://java.sun.com/javase/6/docs/api/java/lang/String.html#replace(char,%20char)]
\[[Green 2008|AA. Bibliography#Green 08]\] ["String.replace"|http://mindprod.com/jgloss/gotchas.html]
\[[Pugh 2009|AA. Bibliography#Pugh 09]\] misusing putIfAbsent
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[!The CERT Oracle Secure Coding Standard for Java^button_arrow_left.png!|Expressions (EXP)] [!The CERT Oracle Secure Coding Standard for Java^button_arrow_up.png!|Expressions (EXP)] [!The CERT Oracle Secure Coding Standard for Java^button_arrow_right.png!|EXP01-J. Do not confuse abstract object equality with reference equality]
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