Incomplete Comparison with Missing Factors

Incomplete Class

Structure: Simple

Description

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.

Extended Description

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.

Common Consequences 1

Scope: IntegrityAccess Control

Impact: Alter Execution LogicBypass Protection Mechanism

Potential Mitigations 1

Phase: Testing

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

Demonstrative Examples 2

ID : DX-115

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.

Code Example:Bad
Java
java

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

ID : DX-116

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.

Code Example:

Bad

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

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 (Improper Authentication).

Any of these passwords would still cause authentication to succeed for the "admin" user:

Code Example:Attack
bash

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 2

CVE-2005-2782PHP remote file inclusion in web application that filters "http" and "https" URLs, but not "ftp".

CVE-2014-6394Product does not prevent access to restricted directories due to partial string comparison with a public directory

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Incorrect Comparison (CWE-697)