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.

Primary

Implementation

Other
Other

Automated Static Analysis
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 searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
High

Implementation
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.)

High

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.

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:

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.

<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";
}

However, the body of the if statement will not be executed, as the "===" compares both the type of the variable AND the value. As the types of the first comparison are number and string, it fails. The types in the second are int and reference, so this one fails as well. The types in the third are reference and string, so it also fails.
While the variables above contain the same values, they are contained in different types, so the document.getElementById... statement will not be executed in any of the cases.
To compare object values, the previous code is modified and shown below to use the "==" for value comparison so the comparison in this example executes the HTML statement:

<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.

var $i = 65;
var $s1 = "65";

if ($i === $s1)
{
echo '($i === $s1) is TRUE'. "\n";
}
else
{
echo '($i === $s1) is FALSE'. "\n";
}

However, the body of the if statement will not be executed, as the "===" compares both the type of the variable AND the value. As the types of the first comparison are number and string, it fails.
While the variables above contain the same values, they are contained in different types, so the TRUE portion of the if statement will not be executed.
To compare object values, the previous code is modified and shown below to use the "==" for value comparison (string converted to number) so the comparison in this example executes the TRUE statement:

var $i = 65;
var $s1 = "65";

if ($i == $s1)
{
echo '($i == $s1) is TRUE'. "\n";
}
else
{
echo '($i == $s1) is FALSE'. "\n";
}

EXP03-J
Do not use the equality operators when comparing values of boxed primitives

EXP03-J
Do not use the equality operators when comparing values of boxed primitives

EXP35-PL
Use the correct operator type for comparing values
CWE More Specific

SFP1
Glitch in computation

Allowed
This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

CWE Content Team
MITRE
2006-12-15
Draft 5
2006-12-15

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Description, Relationships

CWE Content Team
MITRE
2008-10-14
updated Relationships

CWE Content Team
MITRE
2009-05-27
updated Demonstrative_Examples

CWE Content Team
MITRE
2011-03-29
updated Demonstrative_Examples, Description, Potential_Mitigations

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2014-07-30
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2017-11-08
updated Taxonomy_Mappings

CWE Content Team
MITRE
2019-01-03
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2020-08-20
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Demonstrative_Examples, Description, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-04-03
4.17
2025-04-03
updated Demonstrative_Examples

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Weakness_Ordinalities

Erroneous String Compare