CVE-2023-3567 - Linux Kernel Use-After-Free Vulnerability in vc_screen: Insights, Exploit Details, and Mitigation

A recent security vulnerability has been discovered in the Linux Kernel, titled as CVE-2023-3567. This vulnerability exposes a use-after-free flaw specifically within the vcs_read function, located in drivers/tty/vt/vc_screen.c file in vc_screen.

In this post, we will go through an in-depth analysis of the vulnerability, understand the exploit details, and discuss possible mitigation strategies. We will also provide code snippets and links to original references in order to further aid your understanding.

Vulnerability Details and Explanation

A use-after-free issue can result in severe consequences, especially within an environment like the Linux kernel. It occurs when the memory that has been previously released is accessed again. This can lead to code execution, information disclosure, or even system crashes.

In the case of CVE-2023-3567, the vulnerability affects the vcs_read function in the vc_screen component. The specific file involved is drivers/tty/vt/vc_screen.c in the Linux kernel.

An attacker with local user access can potentially exploit this vulnerability to cause a denial of service (i.e., a system crash) or even to leak internal kernel data.

Here's a code snippet from the affected part within vc_screen.c

ssize_t vcs_read(struct file *file, char __user *buf,size_t count, loff_t *ppos)
{
  //...
  buf1 = kmalloc(count, GFP_KERNEL);
  //...
  for (i = ; i < vc->vc_rows; ++i)
  {
    //...
  }
  kfree(buf1);
  return ;
  //...
}

The issue within the vcs_read function lies mainly within the memory allocation for buf1 using kmalloc and then freeing the memory using kfree.

Exploit Details

An attacker who has local user access to a system with a vulnerable Linux kernel can manipulate the behavior of the vcs_read function to trigger the use-after-free flaw.

Original References

1. CVE-2023-3567 on NVD
2. Linux Kernel Git Repository - vc_screen.c
3. Kernel.org Bugzilla – Bug 214759

Mitigation

As of now, there is no official patch or fix available for the CVE-2023-3567 vulnerability in the Linux kernel. However, there are a few steps that can be taken to mitigate the risk associated with this vulnerability.

1. Access Control: Limiting user access to critical systems can act as the first layer of defense. Ensuring that only trusted users have access to sensitive systems can help slow down the rate at which an attacker can exploit this vulnerability.

2. Proactive Monitoring: Continuously monitoring your environment for any suspicious activity will help you detect potential intrusions or exploitation attempts at an early stage. Regularly checking system and kernel logs for any unusual behavior should be a part of your security strategy.

3. Timely OS Updates: Keeping your operating system up-to-date is essential to maintain a secure environment. Ensure that you install the latest security patches and updates available for your Linux distribution.

4. Leveraging Security Tools: Employ security hardening tools, such as SELinux or AppArmor, to provide additional layers of protection to your systems.

Conclusion

CVE-2023-3567 is a critical use-after-free vulnerability in the Linux kernel that can lead to severe consequences if not addressed in a timely manner. Understanding the nature of the flaw and implementing effective mitigation strategies can go a long way in maintaining a secure infrastructure. Always make sure your systems are updated with the latest security patches and follow best security practices to stay safe from such vulnerabilities.

Timeline

Published on: 07/24/2023 16:15:00 UTC
Last modified on: 08/02/2023 00:59:00 UTC