CWE-697 不充分的比较

Incorrect Comparison

结构: Simple

Abstraction: Class

状态: Incomplete

被利用可能性: unkown

基本描述

The software compares two entities in a security-relevant context, but the comparison is incorrect, which may lead to resultant weaknesses.

扩展描述

This weakness class covers several possibilities:

常见的影响

范围	影响	注释
Other	Varies by Context

示例代码

例

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 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.

例

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 C

/ 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

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.

分析过的案例

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