CVE-2023-46813 - Linux Kernel Memory Write Vulnerability and Local Privilege Escalation

A critical security vulnerability (CVE-2023-46813) was discovered in the Linux kernel versions prior to 6.5.9. This vulnerability allows local users with userspace access to MMIO registers to exploit a race condition and gain arbitrary write access to kernel memory, leading to potential privilege escalation. This vulnerability is caused by improper access control in the #VC handler and the Secure Encrypted Virtualization - Encrypted State (SEV-ES) emulation of MMIO accesses.

Details

An issue was discovered in the Linux kernel before 6.5.9 affecting the virtualization support for AMD Secure Encrypted Virtualization - Encrypted State (SEV-ES). The problem arises from incorrect access control enforcement in the #VC handler (Virtualization Exception Handler) and instruction emulation while handling MMIO (Memory-Mapped I/O) accesses.

This kernel vulnerability potentially enables local attackers to exploit a race condition wherein userspace has the ability to replace an instruction just before the #VC handler reads it. As a result, a malicious user could seek arbitrary write access to kernel memory, thereby opening up the possibility for privilege escalation and compromising system security.

Code Snippet

The following code snippet demonstrates the core issue in the vulnerable #VC handler.

static int sev_es_handle_vc(struct kvm_vcpu *vcpu)
{
...
    /* Read instruction from guest memory. */
    rc = kvm_vcpu_read_guest(vcpu, vcpu->arch.swapgs_base, &insn, sizeof(insn));
...
}

The problem lies in the kvm_vcpu_read_guest() function. Due to the race condition, userspace has the opportunity to replace an instruction just before the #VC handler reads it through this function.

Original References

It is highly recommended for system administrators and kernel developers to review the following original references and announcements for a deeper understanding of the vulnerability (CVE-2023-46813):

1. The Linux kernel source code: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
2. The official commit addressing the issue: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=...
3. The CVE details page: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-46813

Exploit Details

At the time of writing, there are no publicly known exploits specifically targeting CVE-2023-46813. However, given the potential severity of this vulnerability, it is critical for system administrators and kernel developers to proactively apply patches and mitigate the risk.

To ensure system security and avoid the exploit of this vulnerability, you can take the following actions:

1. Update the Linux kernel to the latest version (6.5.9 or later), as it includes patches and fixes for the issue.

2. As a temporary measure, restrict user access to MMIO registers by using stricter access control policies and maintaining a close watch on user activities.

In conclusion, CVE-2023-46813 is a critical vulnerability that could potentially lead to privilege escalation and compromise system security. By understanding the details of this vulnerability and applying the necessary patches, you can protect your systems and maintain a secure environment.

Timeline

Published on: 10/27/2023 03:15:08 UTC
Last modified on: 11/07/2023 20:42:02 UTC