CWE-558: Use of getlogin() in Multithreaded Application

What is Use of getlogin() in Multithreaded Application?

• Overview: This vulnerability involves using the getlogin() function in a multithreaded application, which may lead to incorrect or unreliable user information being returned because the function is not thread-safe and can be altered by other processes.

• Exploitation Methods:

• Attackers can exploit this by causing a race condition where the getlogin() function returns a wrong username.
• Common attack patterns include manipulating the environment to change the username information between threads, potentially leading to incorrect privilege assignments.

• Security Impact:

• Direct consequences include the application using incorrect user credentials, leading to unauthorized access or actions.
• Potential cascading effects involve compromised authentication, incorrect logging, or misattribution of actions.
• Business impact could include data breaches, loss of user trust, legal liabilities, and financial losses.

• Prevention Guidelines:

• Specific code-level fixes include using thread-safe alternatives like getpwuid(geteuid()) instead of getlogin().
• Security best practices involve avoiding non-reentrant functions in multithreaded applications and ensuring proper synchronization.
• Recommended tools and frameworks include static analysis tools to detect unsafe function use and libraries that offer safer threading primitives.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

Certainly! Here's an improved version of the content, addressing the issues you've mentioned:

C Example

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>

void *print_username(void *arg) {
    // Vulnerable code: getlogin() is not thread-safe
    // It relies on static storage which can be overwritten by other threads,
    // leading to incorrect values or undefined behavior in multithreaded applications.
    const char *username = getlogin();
    if (username != NULL) {
        printf("Logged in as: %s\n", username);
    } else {
        perror("getlogin error");
    }
    return NULL;
}

int main() {
    pthread_t thread1, thread2;

    // Creating multiple threads that will call getlogin()
    pthread_create(&thread1, NULL, print_username, NULL);
    pthread_create(&thread2, NULL, print_username, NULL);

    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);

    return 0;
}

How to fix Use of getlogin() in Multithreaded Application?

The getlogin() function is not thread-safe because it depends on static storage, which can be altered by concurrent threads. This can cause it to return incorrect or inconsistent results in a multithreaded context. To address this issue, use getpwuid_r(), a reentrant and thread-safe alternative that retrieves the user's login name based on their user ID. The user ID can be obtained using geteuid() for the effective user ID.

Fixed Code Example

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/types.h>
#include <pwd.h>
#include <stdlib.h>
#include <string.h>

void *print_username(void *arg) {
    // Fixed code: Using getpwuid_r for thread-safe user name retrieval
    uid_t uid = geteuid(); // Get effective user ID
    struct passwd pwd;
    struct passwd *result;
    char buffer[1024];
    int ret;

    // Use getpwuid_r to safely retrieve user information
    ret = getpwuid_r(uid, &pwd, buffer, sizeof(buffer), &result);
    if (result == NULL) {
        if (ret == 0) {
            printf("User not found\n");
        } else {
            perror("getpwuid_r error");
        }
    } else {
        printf("Logged in as: %s\n", pwd.pw_name);
    }
    return NULL;
}

int main() {
    pthread_t thread1, thread2;

    // Creating multiple threads that will call getpwuid_r()
    pthread_create(&thread1, NULL, print_username, NULL);
    pthread_create(&thread2, NULL, print_username, NULL);

    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);

    return 0;
}

Explanation:

• Vulnerability: The original code uses getlogin(), which is not safe in a multithreaded application due to its reliance on static storage. This can lead to incorrect user names or undefined behavior when accessed by multiple threads concurrently.

• Fix: The revised code uses getpwuid_r(), which is thread-safe and does not rely on shared static storage. This function retrieves user information based on the user ID, obtained through geteuid(). By using getpwuid_r(), each thread independently manages its own storage, ensuring safe and consistent retrieval of the username.