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.)
CWE-597 Variant Draft
Use of Wrong Operator in String Comparison
This vulnerability occurs when a developer incorrectly compares string values, typically by using reference equality operators (like == or !=) instead of dedicated string comparison methods (like…
Definition
What is CWE-597?
This vulnerability occurs when a developer incorrectly compares string values, typically by using reference equality operators (like == or !=) instead of dedicated string comparison methods (like .equals()).
In languages like Java, using '==' to compare strings checks if two object references point to the same memory location, not whether their textual content is identical. This is a common logic error because two separate string objects with the same characters will fail an '==' test, leading to unexpected program behavior and flawed conditional logic.
While this often results in general bugs or incorrect functionality, it becomes a security issue when the flawed comparison is part of an authentication check, authorization decision, or input validation. An attacker could potentially bypass security controls by exploiting the unintended mismatch, turning a simple coding mistake into a system vulnerability.
Real-world impact
Real-world CVEs caused by CWE-597
No public CVE references are linked to this CWE in MITRE's catalog yet.
How attackers exploit it
Step-by-step attacker path
- 1
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.
- 2
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:
- 3
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.
- 4
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:
- 5
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.
Vulnerable code example
Vulnerable Java
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");
} Secure code example
Secure Java
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");
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-597
- 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.)
Detection signals
How to detect CWE-597
CWE-597
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Frequently asked questions What is CWE-597?
How serious is CWE-597?
What languages or platforms are affected by CWE-597?
How can I prevent CWE-597?
How does Plexicus detect and fix CWE-597?
Where can I learn more about CWE-597?
Frequently asked questions
What is CWE-597?
This vulnerability occurs when a developer incorrectly compares string values, typically by using reference equality operators (like == or !=) instead of dedicated string comparison methods (like .equals()).
How serious is CWE-597?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-597?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-597?
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.)
How does Plexicus detect and fix CWE-597?
Plexicus's SAST engine matches the data-flow signature for CWE-597 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-597?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/597.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-597
CWE-595 Parent
Comparison of Object References Instead of Object Contents
This vulnerability occurs when code incorrectly checks if two object references point to the same memory location, rather than comparing…
CWE-1097 Sibling
Persistent Storable Data Element without Associated Comparison Control Element
This weakness occurs when a persistent data object lacks the necessary methods to be properly compared, which can lead to inconsistent or…
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