CVE-2023-6546 - Race Condition Vulnerability in Linux GSM 071 TTY Multiplexer: Exploit Details, Code Examples, and Security Recommendations

A recent security issue has been discovered in the Linux kernel, named CVE-2023-6546. This vulnerability affects the GSM 071 TTY Multiplexer, which is commonly used in mobile communication systems for exchanging data and signaling information between devices. The purpose of this article is to provide an in-depth explanation of the vulnerability, share code snippets, discuss the potential impact, and suggest steps for mitigation.

The Vulnerability

The CVE-2023-6546 vulnerability is caused by a race condition in the GSM 071 TTY Multiplexer of the Linux kernel. This race condition occurs when two threads execute the GSMIOC_SETCONF ioctl on the same TTY file descriptor with the GSM line discipline enabled. As a result, a use-after-free problem can occur on a struct gsm_dlci while restarting the GSM mux, allowing a local unprivileged user to escalate their privileges on the system.

The following code snippet demonstrates the vulnerability

struct gsm_netconfig {
    __u32 adaption;
    __u32 encapsulation;
    __u8 initiator;
    __u8 clocal;
    __u8 burst;
    __u8 filler[3];
};

// Vulnerable ioctl handler
static int gsm_ioctl(struct tty_struct *tty, struct file *file,
                     unsigned int cmd, unsigned long arg)
{
    struct gsm_mux *gsm = NULL;
    struct gsm_netconfig nc;

    // … 
    
    case GSMIOC_SETCONF:
        if (copy_from_user(&nc, uarg, sizeof(nc)))
            return -EFAULT;
        err = gsmld->ops->set_config(gsmld, &nc);
        break;

    // …
}

More information about the vulnerability can be found in the following references

1. CVE-2023-6546 - Race condition in Linux GSM 071 TTY Multiplexer
2. Kernel.org - Linux kernel source code repository
3. GSM 07.10 - Multiplexer for the GSM Digital Cellular System (DCS 180)

Potential Exploit and Impact

Unprivileged users could exploit this vulnerability by running a specially crafted program that triggers the race condition. When successful, the attacker gains higher access levels and can execute malicious tasks (e.g., spying on sensitive data, causing a denial-of-service condition, or executing arbitrary code) with elevated privileges.

This vulnerability poses a serious risk to the security and privacy of affected systems and users, as it could lead to unauthorized access, information leakage, and potential remote attacks.

To protect your systems from this vulnerability, we recommend the following actions

1. Keep your Linux kernel up-to-date. The latest kernel versions often include security fixes and improvements. Consult your distribution's documentation and update mechanisms to ensure your kernel is current.
2. Restrict the use of the GSMIOC_SETCONF ioctl to trusted users and applications. Configure your system's security policies to limit the access and control of system resources, especially those related to GSM communications.
3. Monitor system logs and usage patterns to detect any suspicious activity. Employ intrusion detection systems to safeguard your environment and promptly respond to security breaches.

In addition, developers and maintainers of the Linux kernel are encouraged to thoroughly review and test the GSM 071 TTY Multiplexer code to address this vulnerability and prevent similar issues in the future.

By understanding the details and potential impact of CVE-2023-6546, administrators and users can take the necessary precautions to protect their systems and maintain the security of their environments.

Timeline

Published on: 12/21/2023 20:15:08 UTC
Last modified on: 02/28/2024 15:15:07 UTC