The product performs a comparison between entities that must consider multiple factors or characteristics of each entity, but the comparison does not include one or more of these factors.

Primary

Implementation

Integrity
Access Control
Alter Execution Logic
Bypass Protection Mechanism
An incomplete comparison can lead to resultant weaknesses, e.g., by operating on the wrong object or making a security decision without considering a required factor.

Testing
Thoroughly test the comparison scheme before deploying code into production. Perform positive testing as well as negative testing.

Consider an application in which Truck objects are defined to be the same if they have the same make, the same model, and were manufactured in the same year.

public class Truck {
private String make;private String model;private int year;
public boolean equals(Object o) {
if (o == null) return false;if (o == this) return true;if (!(o instanceof Truck)) return false;
Truck t = (Truck) o;
return (this.make.equals(t.getMake()) && this.model.equals(t.getModel()));
}
}

Here, the equals() method only checks the make and model of the Truck objects, but the year of manufacture is not included.

This example defines a fixed username and password. The AuthenticateUser() function is intended to accept a username and a password from an untrusted user, and check to ensure that it matches the username and password. If the username and password match, AuthenticateUser() is intended to indicate that authentication succeeded.

/* Ignore CWE-259 (hard-coded password) and CWE-309 (use of password system for authentication) for this example. */

char *username = "admin";char *pass = "password";
int AuthenticateUser(char *inUser, char *inPass) {if (strncmp(username, inUser, strlen(inUser))) {logEvent("Auth failure of username using strlen of inUser");return(AUTH_FAIL);}if (! strncmp(pass, inPass, strlen(inPass))) {logEvent("Auth success of password using strlen of inUser");return(AUTH_SUCCESS);}else {logEvent("Auth fail of password using sizeof");return(AUTH_FAIL);}}
int main (int argc, char **argv) {
int authResult;if (argc < 3) {ExitError("Usage: Provide a username and password");}authResult = AuthenticateUser(argv[1], argv[2]);if (authResult == AUTH_SUCCESS) {DoAuthenticatedTask(argv[1]);}else {ExitError("Authentication failed");}}

In AuthenticateUser(), the strncmp() call uses the string length of an attacker-provided inPass parameter in order to determine how many characters to check in the password. So, if the attacker only provides a password of length 1, the check will only examine the first byte of the application's password before determining success.
As a result, this partial comparison leads to improper authentication (CWE-287).
Any of these passwords would still cause authentication to succeed for the "admin" user:

ppapaspass

This significantly reduces the search space for an attacker, making brute force attacks more feasible.
The same problem also applies to the username, so values such as "a" and "adm" will succeed for the username.
While this demonstrative example may not seem realistic, see the Observed Examples for CVE entries that effectively reflect this same weakness.

CVE-2005-2782
PHP remote file inclusion in web application that filters "http" and "https" URLs, but not "ftp".
https://www.cve.org/CVERecord?id=CVE-2005-2782

CVE-2014-6394
Product does not prevent access to restricted directories due to partial string comparison with a public directory
https://www.cve.org/CVERecord?id=CVE-2014-6394

Allowed-with-Review
This CWE entry is a Class and might have Base-level children that would be more appropriate
Examine children of this entry to see if there is a better fit

CWE Content Team
MITRE
2018-01-04
3.1
2018-03-29

CWE Content Team
MITRE
2019-01-03
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Description, Relationships, Type

CWE Content Team
MITRE
2021-03-15
updated Demonstrative_Examples

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Observed_Examples

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