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.
Extended Description
For example, an attacker might succeed in authentication by providing a small password that matches the associated portion of the larger, correct password.
Time of Introduction
Implementation
Applicable Platforms
Languages
All
Common Consequences
Scope
Effect
Integrity
Access Control
Technical Impact: Alter execution
logic; Bypass protection
mechanism
Demonstrative Examples
Example 1
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 Code)
Example
Language: 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.
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.
Description
