CWE-187 部分比较

Partial String Comparison

结构: Simple

Abstraction: Variant

状态: Incomplete

被利用可能性: unkown

基本描述

The software performs a comparison that only examines a portion of a factor before determining whether there is a match, such as a substring, leading to resultant weaknesses.

扩展描述

For example, an attacker might succeed in authentication by providing a small password that matches the associated portion of the larger, correct password.

相关缺陷

  • cwe_Nature: ChildOf cwe_CWE_ID: 1023 cwe_View_ID: 1000 cwe_Ordinal: Primary

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

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

标识 说明 链接
CVE-2014-6394 Product does not prevent access to restricted directories due to partial string comparison with a public directory https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-6394
CVE-2004-1012 Argument parser of an IMAP server treats a partial command "body[p" as if it is "body.peek", leading to index error and out-of-bounds corruption. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-1012
CVE-2004-0765 Web browser only checks the hostname portion of a certificate when the hostname portion of the URI is not a fully qualified domain name (FQDN), which allows remote attackers to spoof trusted certificates. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-0765
CVE-2002-1374 One-character password by attacker checks only against first character of real password. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2002-1374
CVE-2000-0979 One-character password by attacker checks only against first character of real password. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2000-0979

Notes

分类映射

映射的分类名 ImNode ID Fit Mapped Node Name
PLOVER Partial Comparison