Linux Kernel effected by CVE-2023-2163

CVE-2023-2163 is a critical vulnerability in the Linux Kernel, specifically affecting kernel versions 5.4 and above (excluding 6.3). This vulnerability arises from incorrect verifier pruning in the Berkeley Packet Filter (BPF), leading to unsafe code paths being incorrectly marked as safe.  The vulnerability has a CVSS v3.1 Base Score of 8.8, indicating its high severity. The consequences are arbitrary read/write in kernel memory, lateral privilege escalation and container escape. 

How CVE-2023-2163 is being exploited

Attackers exploit CVE-2023-2163 by leveraging the incorrect verifier pruning in BPF to perform arbitrary read/write operations in kernel memory. This allows them to escalate privileges within the system and potentially even escape containerized environments. For example, an attacker can craft a malicious BPF program that bypasses the verifier checks and executes unsafe code paths. 

The following code snippet is an example that demonstrates how an attacker might exploit this vulnerability by attempting to write to an arbitrary memory address, which could lead to privilege escalation:

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>

SEC("xdp")
int exploit(struct xdp_md *ctx) {
    char *ptr = (char *)0xdeadbeef; // Arbitrary address
    *ptr = 'A'; // Arbitrary write
    return XDP_PASS;
}

char _license[] SEC("license") = "GPL";

How to fix CVE-2023-2163

Where possible, move to a version of your Linux distribution where this vulnerability has been fixed. You can find a list of fixed Ubuntu Linux versions on their related security page. You can also fix CVE-2023-2163 by updating the Linux Kernel to a version where the vulnerability has been patched. Technical details for a patch can be found in the official Linux Kernel repository.

How to prevent similar vulnerabilities in the future

Preventing similar vulnerabilities involves improving the verification processes for BPF programs. Regularly update the kernel and apply security patches promptly. Conduct thorough code reviews and use static analysis tools to detect potential flaws in the verifier logic. Additionally, consider implementing runtime checks to monitor and restrict BPF program behavior.

Summary

CVE-2023-2163 is a high-severity vulnerability in the Linux Kernel due to incorrect verifier pruning in BPF. It allows arbitrary read/write in kernel memory, leading to privilege escalation and container escape. Exploiting this vulnerability involves crafting malicious BPF programs that bypass verifier checks. Fixing it requires updating the kernel to a patched version. 

For a more detailed technical analysis visit the related Google Security Blog: “A Deep Dive into CVE-2023-2163”.