CWE-558: Use of getlogin() in Multithreaded Application
Use of getlogin() in Multithreaded Application
Weakness ID: 558 (Weakness Variant)
Status: Draft
Description
Description Summary
The application uses the getlogin() function in a multithreaded
context, potentially causing it to return incorrect
values.
Extended Description
The getlogin() function returns a pointer to a string that contains the
name of the user associated with the calling process. The function is not
reentrant, meaning that if it is called from another process, the contents
are not locked out and the value of the string can be changed by another
process. This makes it very risky to use because the username can be changed
by other processes, so the results of the function cannot be trusted.
Time of Introduction
Implementation
Applicable Platforms
Languages
C
C++
Demonstrative Examples
Example 1
The following code relies on getlogin() to determine whether or not
a user is trusted. It is easily subverted.
(Bad Code)
C
pwd = getpwnam(getlogin());
if (isTrustedGroup(pwd->pw_gid)) {
allow();
} else {
deny();
}
Potential Mitigations
Phase
Description
Using names for security purposes is not advised. Names are easy to
forge and can have overlapping user IDs, potentially causing confusion
or impersonation.
Use getlogin_r() instead, which is reentrant, meaning that other
processes are locked out from changing the username.
Description
