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Variant · Low-Medium

CWE-597: Use of Wrong Operator in String Comparison

The product uses the wrong operator when comparing a string, such as using "==" when the .equals() method should be used instead.

CWE-597 · Variant Level ·1 Mitigations

Description

The product uses the wrong operator when comparing a string, such as using "==" when the .equals() method should be used instead.

In Java, using == or != to compare two strings for equality actually compares two objects for equality rather than their string values for equality. Chances are good that the two references will never be equal. While this weakness often only affects program correctness, if the equality is used for a security decision, the unintended comparison result could be leveraged to affect program security.

Potential Impact

Other

Other

Demonstrative Examples

In the example below, two Java String objects are declared and initialized with the same string values. An if statement is used to determine if the strings are equivalent.
Bad
String str1 = new String("Hello");String str2 = new String("Hello");if (str1 == str2) {System.out.println("str1 == str2");}
However, the if statement will not be executed as the strings are compared using the "==" operator. For Java objects, such as String objects, the "==" operator compares object references, not object values. While the two String objects above contain the same string values, they refer to different object references, so the System.out.println statement will not be executed. To compare object values, the previous code could be modified to use the equals method:
Good
if (str1.equals(str2)) {System.out.println("str1 equals str2");}
In the example below, three JavaScript variables are declared and initialized with the same values. Note that JavaScript will change a value between numeric and string as needed, which is the reason an integer is included with the strings. An if statement is used to determine whether the values are the same.
Bad
<p id="ieq3s1" type="text">(i === s1) is FALSE</p>
                  <p id="s4eq3i" type="text">(s4 === i) is FALSE</p>
                  <p id="s4eq3s1" type="text">(s4 === s1) is FALSE</p>
                  
                  var i = 65;
                  var s1 = '65';
                  var s4 = new String('65');
                  
                  if (i === s1)
                  {
                  document.getElementById("ieq3s1").innerHTML = "(i === s1) is TRUE";
                  }
                  
                  if (s4 === i)
                  {
                  document.getElementById("s4eq3i").innerHTML = "(s4 === i) is TRUE";
                  }
                  
                  if (s4 === s1)
                  {
                  document.getElementById("s4eq3s1").innerHTML = "(s4 === s1) is TRUE";
                  }
Good
<p id="ieq2s1" type="text">(i == s1) is FALSE</p>
                  <p id="s4eq2i" type="text">(s4 == i) is FALSE</p>
                  <p id="s4eq2s1" type="text">(s4 == s1) is FALSE</p>
                  
                  var i = 65;
                  var s1 = '65';
                  var s4 = new String('65');
                  
                  if (i == s1)
                  {
                  document.getElementById("ieq2s1").innerHTML = "(i == s1) is TRUE";
                  }
                  
                  if (s4 == i)
                  {
                  document.getElementById("s4eq2i").innerHTML = "(s4 == i) is TRUE";
                  }
                  
                  if (s4 == s1)
                  {
                  document.getElementById("s4eq2s1").innerHTML = "(s4 == s1) is TRUE";
                  }
In the example below, two PHP variables are declared and initialized with the same numbers - one as a string, the other as an integer. Note that PHP will change the string value to a number for a comparison. An if statement is used to determine whether the values are the same.
Bad
var $i = 65;
                  var $s1 = "65";
                  
                  if ($i === $s1)
                  {
                  echo '($i === $s1) is TRUE'. "\n";
                  }
                  else
                  {
                  echo '($i === $s1) is FALSE'. "\n";
                  }
Good
var $i = 65;
                  var $s1 = "65";
                  
                  if ($i == $s1)
                  {
                  echo '($i == $s1) is TRUE'. "\n";
                  }
                  else
                  {
                  echo '($i == $s1) is FALSE'. "\n";
                  }

Mitigations & Prevention

Implementation High

Within Java, use .equals() to compare string values. Within JavaScript, use == to compare string values. Within PHP, use == to compare a numeric value to a string value. (PHP converts the string to a number.)

Detection Methods

  • Automated Static Analysis High — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea

CWE-595: Comparison of Object References Instead of Object Contents

The product compares object references instead of the contents of the objects themselves, preventing it from detecting e...

CWE-480: Use of Incorrect Operator

The product accidentally uses the wrong operator, which changes the logic in security-relevant ways.

Taxonomy Mappings

  • The CERT Oracle Secure Coding Standard for Java (2011): EXP03-J — Do not use the equality operators when comparing values of boxed primitives
  • The CERT Oracle Secure Coding Standard for Java (2011): EXP03-J — Do not use the equality operators when comparing values of boxed primitives
  • SEI CERT Perl Coding Standard: EXP35-PL — Use the correct operator type for comparing values
  • Software Fault Patterns: SFP1 — Glitch in computation

Frequently Asked Questions

What is CWE-597?

CWE-597 (Use of Wrong Operator in String Comparison) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product uses the wrong operator when comparing a string, such as using "==" when the .equals() method should be used instead.

How can CWE-597 be exploited?

Attackers can exploit CWE-597 (Use of Wrong Operator in String Comparison) to other. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-597?

Key mitigations include: Within Java, use .equals() to compare string values. Within JavaScript, use == to compare string values. Within PHP, use == to compare a numeric value to a string value

What is the severity of CWE-597?

CWE-597 is classified as a Variant-level weakness (Low-Medium abstraction). Its actual severity depends on the specific context and how the weakness manifests in your application.