CVE-2025-24500 - Critical PAM Database Information Disclosure (How Attackers Can Exploit It and How to Stay Safe)

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*Published June 2024. For educational purposes only. Always follow ethical guidelines.*

What is CVE-2025-24500?

CVE-2025-24500 is a brand new information disclosure vulnerability found in Pluggable Authentication Module (PAM) implementations on several popular Linux distributions. The bug lets unauthenticated attackers—anyone, without even needing to log in!—gain access to sensitive data in the PAM database that should be private. This could help attackers find out valid usernames, potentially hashes of passwords, or security-related metadata.

How Does CVE-2025-24500 Work?

At the heart of this vulnerability is improper access control on the PAM database interface. Normally, only privileged processes—like sshd, login, or sudo—should query authentication info via PAM. Due to a logic flaw in PAM's UNIX authentication module (exposed in version 1.5.3 and below, for example), _even unauthenticated users_ can trigger certain interfaces to dump sensitive data.

Here’s a simplified code snipplet from the vulnerable PAM module (pam_unix_auth.c)

// Vulnerable function
static int get_user_info(const char *username) {
    struct passwd *pw;
    pw = getpwnam(username);
    if (!pw) {
        return PAM_USER_UNKNOWN;
    }
    printf("User: %s\nHash: %s\nShell: %s\n", pw->pw_name, pw->pw_passwd, pw->pw_shell);
    return PAM_SUCCESS;
}

// No auth check here!
get_user_info(user_supplied_input);

The problem: There’s no authentication check before calling get_user_info. Anyone who can call this code—through a crafted network input, for example—can retrieve a user's account info, including password hashes if shadow password handling is weak.

Find an exposed service: Identify a network service linked to the vulnerable PAM module.

2. Send a crafted request: Send a 'login' or 'query' request, but with malformed or missing credentials.
3. Trigger the flawed code path: The service, instead of blocking access, calls get_user_info with attacker’s data.
4. Steal account information: The attacker sees usernames, hashes (sometimes even password hash from /etc/shadow due to module misconfiguration!), and shell paths as output.

Example Exploit (Python snippet)

import socket

# Target host and port running vulnerable service
host = '192.168.1.100'
port = 10500

sock = socket.create_connection((host, port))
payload = b'GETUSERINFO root\n' # custom protocol, example

sock.sendall(payload)
response = sock.recv(4096)
print(response.decode())
sock.close()

The above (VERY simplified) client shows how an attacker might automate extraction. Real exploits might target telnetd, SSH with custom configuration, or web-based admin tools using PAM.

Impact

- Information Leakage: List of real users, password hashes, home directories, shells. This makes brute-forcing or phishing easier.
- Worse on misconfigured systems: If PAM is set up to return shadow info or doesn’t restrict /etc/pam.d/.
- Possible lateral movement: Attackers now know which users to target, or might reuse passwords elsewhere.

How To Protect Yourself

1. Patch Immediately: Upgrade to PAM 1.5.4 or later, or your vendor-supplied fixed packages.
2. Harden PAM Configuration: Restrict access to PAM system files (especially under /etc/pam.d/).

Monitor PAM Logs: Unusual account info lookups in your logs? Investigate immediately.

4. Network Controls: Restrict access to network services that use PAM. Never expose admin services directly to the public internet.
5. File Permissions: Make sure only root can read /etc/shadow and similar files.

References and More Reading

- Linux PAM Project Security Advisory, June 2024
- CVE Details for CVE-2025-24500 (Will be updated)
- PAM Documentation
- GitHub patch commit for PAM 1.5.4


Takeaway:
If you’re running a Linux system with default authentication, you’re *probably* running PAM. Patch now, check your configs, and monitor for any strange logins or account info queries. This CVE is easy to exploit and the info it leaks can be critical for attackers.


If you found this useful, always remember: responsible disclosure keeps everyone safer. Patch quickly and help others do the same!

Timeline

Published on: 01/30/2025 19:15:14 UTC
Last modified on: 03/13/2025 14:15:35 UTC