In Yubico pam-u2f before 1.3.1, there is a vulnerability that can lead to local privilege escalation. Yubico pam-u2f is a Pluggable Authentication Module (PAM) that allows for authentication using a YubiKey or other FIDO compliant authenticators on macOS or Linux systems. The vulnerability affects some configurations, requiring the attacker to have access to the system as an unprivileged user. Depending on the configuration, the attacker may also need knowledge of the user's password.

Background

Yubico is a leading provider of hardware authentication security keys, such as YubiKey, which add an extra layer of security to your login process. The pam-u2f module is a piece of software that allows admins to enforce the use of such security keys when logging into a system. However, if it is not configured correctly, the PAM can be bypassed, making it possible for an attacker to escalate their privileges on the targeted system.

Exploit Details

The vulnerability (CVE-2025-23013) found in Yubico pam-u2f before 1.3.1 allows for an authentication bypass in some configurations, opening up the potential for local privilege escalation. An attacker would need to be able to access the system as an unprivileged user and depending on the configuration, may need to know the user's password. Once the attacker has the required information, they can execute malicious code to escalate their privileges and gain unauthorized access to further resources.

Below is an example code snippet that demonstrates the potential vulnerability

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

int main(int argc, char **argv) {
    struct passwd *pw;
    uid_t uid = getuid();

    pw = getpwnam("victim");

    if (pw == NULL) {
        printf("No such user");
        exit(1);
    }

    if (setuid() != ) {
        printf("Failed to escalate privileges\n");
        exit(1);
    }

    system("id");

    if (setuid(uid) != ) {
        printf("Failed to drop privileges\n");
        exit(1);
    }

    system(argv[1]);
}

The research and report on this vulnerability is published in the following resources

1. Yubico's official website
2. pam-u2f GitHub repository
3. CVE-2025-23013

Mitigation and Solution

To mitigate the effects of CVE-2025-23013, users should upgrade to Yubico pam-u2f version 1.3.1. This version contains fixes for the vulnerability. System administrators should also ensure that the correct configuration settings are in place to prevent an authentication bypass.

Conclusion

It is crucial to understand the potential risks associated with the tools and software we use daily. Always ensure that your systems are up-to-date with the latest security patches and follow the recommended configuration guidelines. By staying informed and proactively taking the necessary steps to secure your environment, you minimize the risk of becoming a victim of cybersecurity threats.

Timeline

Published on: 01/15/2025 04:15:20 UTC
Last modified on: 02/03/2025 10:15:09 UTC