CWE-1023 缺失要素致使对比不完全

Incomplete Comparison with Missing Factors

结构: Simple

Abstraction: Base

状态: Incomplete

被利用可能性: unkown

基本描述

The software 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. This can lead to resultant weaknesses, e.g. by operating on the wrong object.

相关缺陷

ChildOf: CWE-184 | 不完整的黑名单

ChildOf: CWE-187 | 部分比较

ChildOf: CWE-478 | 在Switch语句中缺失缺省条件

ChildOf: CWE-839 | 未进行最小值检查的数值范围比较

适用平台

Language: {'cwe_Class': 'Language-Independent', 'cwe_Prevalence': 'Undetermined'}

常见的影响

范围 影响 注释
['Integrity', 'Access Control'] ['Alter Execution Logic', 'Bypass Protection Mechanism']

可能的缓解方案

Testing

策略:

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

示例代码

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.

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