CWE-1023: Incomplete Comparison with Missing Factors

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.

Potential Impact

Integrity, Access Control

Alter Execution Logic, Bypass Protection Mechanism

Demonstrative Examples

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

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.

Bad

/* 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

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.

Detection Methods

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

Real-World CVE Examples

CVE ID	Description
CVE-2005-2782	PHP remote file inclusion in web application that filters "http" and "https" URLs, but not "ftp".
CVE-2014-6394	Product does not prevent access to restricted directories due to partial string comparison with a public directory

Frequently Asked Questions

What is CWE-1023?

CWE-1023 (Incomplete Comparison with Missing Factors) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Class-level weakness. 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.

How can CWE-1023 be exploited?

Attackers can exploit CWE-1023 (Incomplete Comparison with Missing Factors) to alter execution logic, bypass protection mechanism. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-1023?

Follow secure coding practices, conduct code reviews, and use automated security testing tools (SAST/DAST) to detect this weakness early in the development lifecycle.

What is the severity of CWE-1023?

CWE-1023 is classified as a Class-level weakness (High abstraction). It has been observed in 2 real-world CVEs.