CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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ID

CWE-697: Incorrect Comparison

Weakness ID: 697
Abstraction: Class
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.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
NatureTypeIDName
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).1000Research Concepts
ParentOfBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.183Permissive Whitelist
ParentOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More general than a Base weakness.185Incorrect Regular Expression
ParentOfBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.581Object Model Violation: Just One of Equals and Hashcode Defined
ParentOfBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.1023Incomplete Comparison with Missing Factors
ParentOfBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.1024Comparison of Incompatible Types
ParentOfBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.1025Comparison Using Wrong Factors
ParentOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More general than a Base weakness.1039Automated Recognition Mechanism with Inadequate Detection or Handling of Adversarial Input Perturbations
CanFollowVariantVariant - a weakness that is described at a very low level of detail, typically limited to a specific language or technology. More specific than a Base weakness.481Assigning instead of Comparing
+ Relevant to the view "Development Concepts" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.171Cleansing, Canonicalization, and Comparison Errors
ParentOfBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.1023Incomplete Comparison with Missing Factors
ParentOfBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.1024Comparison of Incompatible Types
ParentOfBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.1025Comparison Using Wrong Factors
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

PhaseNote
Implementation
+ Common Consequences

The table below 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.

ScopeImpactLikelihood
Other

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");
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:

(attack code)
 
p
pa
pas
pass

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
ReferenceDescription
Proxy performs incorrect comparison of request headers, leading to infoleak
+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
+ Memberships
This 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.
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.747CERT C Secure Coding (2008 Version) Section 49 - 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
+ Notes

Maintenance

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
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
Previous Entry Names
Change DatePrevious Entry Name
2018-03-27Insufficient Comparison

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Page Last Updated: March 29, 2018