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CWE-697: Incorrect Comparison

Weakness ID: 697
Abstraction: Pillar
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software compares two entities in a security-relevant context, but the comparison is incorrect, which may lead to resultant weaknesses.
+ Extended Description

This weakness class covers several possibilities:

  1. the comparison checks one factor incorrectly;
  2. the comparison should consider multiple factors, but it does not check some of those factors at all;
  3. the comparison checks the wrong factor.
+ Modes Of Introduction
Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
+ Applicable Platforms
Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Class: Language-Independent (Undetermined Prevalence)


Class: Technology-Independent (Undetermined Prevalence)

+ Common Consequences
Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Technical Impact: Varies by Context

+ Demonstrative Examples

Example 1

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.

(bad code)
Example Language: Java 
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.

Example 2

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.

(bad code)
Example Language:
/* 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");
if (! strncmp(pass, inPass, strlen(inPass))) {
logEvent("Auth success of password using strlen of inUser");
else {
logEvent("Auth fail of password using sizeof");

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) {
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:

(attack code)

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.

+ Observed Examples
Proxy performs incorrect comparison of request headers, leading to infoleak
+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
+ Memberships
Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.747CERT C Secure Coding Standard (2008) Chapter 14 - Miscellaneous (MSC)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.883CERT C++ Secure Coding Section 49 - Miscellaneous (MSC)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.977SFP Secondary Cluster: Design
MemberOfViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).1003Weaknesses for Simplified Mapping of Published Vulnerabilities
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1140SEI CERT Oracle Secure Coding Standard for Java - Guidelines 06. Methods (MET)
+ Notes


This entry likely has some relationships with case sensitivity (CWE-178), but case sensitivity is a factor in other types of weaknesses besides comparison. Also, in cryptography, certain attacks are possible when certain comparison operations do not take place in constant time, causing a timing-related information leak (CWE-208).
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2008-09-09CWE Content TeamMITRE
+ Modifications
Modification DateModifierOrganization
2008-11-24CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2009-03-10CWE Content TeamMITRE
updated Related_Attack_Patterns
2009-05-27CWE Content TeamMITRE
updated Description
2011-03-29CWE Content TeamMITRE
updated Description
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2011-09-13CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Related_Attack_Patterns, Relationships
2014-07-30CWE Content TeamMITRE
updated Relationships
2017-05-03CWE Content TeamMITRE
updated Related_Attack_Patterns
2017-11-08CWE Content TeamMITRE
updated Taxonomy_Mappings
2018-03-27CWE Content TeamMITRE
updated Common_Consequences, Demonstrative_Examples, Description, Maintenance_Notes, Name, Observed_Examples, Relationships
2019-01-03CWE Content TeamMITRE
updated Related_Attack_Patterns, Relationships
2019-06-20CWE Content TeamMITRE
updated Related_Attack_Patterns
2019-09-19CWE Content TeamMITRE
updated Relationships
2020-02-24CWE Content TeamMITRE
updated Applicable_Platforms, Relationships, Type
2020-06-25CWE Content TeamMITRE
updated Relationships
2020-08-20CWE Content TeamMITRE
updated Related_Attack_Patterns
+ Previous Entry Names
Change DatePrevious Entry Name
2018-03-27Insufficient Comparison
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Page Last Updated: October 26, 2021