CVE-2023-2163 - BPF Vulnerability in Linux Kernel 5.4 and Later Lateral Privilege Escalation, Container Escape, and Arbitrary Kernel Memory Access

A newly discovered vulnerability, tracked as CVE-2023-2163, affects the Linux kernel, specifically its implementation of eBPF (extended Berkeley Packet Filter). This vulnerability impacts kernel versions 5.4 and later and potentially results in several security threats. Among these are arbitrary kernel memory read/write, lateral privilege escalation, and container escape. This post aims to provide an in-depth understanding of the issue, including code snippets, links to the original references, and details about the exploit.

Background

eBPF is a powerful subsystem incorporated in the Linux kernel. It enables the running of sandboxed programs within the kernel context, providing several use-cases such as observability, network filtering, and security enforcement. However, there is a flaw in the implementation of the 'verifier' component in eBPF. This component is responsible for ensuring that the provided eBPF program does not pose security risks to the kernel.

Vulnerability Details

The vulnerability results from incorrect pruning performed by the verifier component in eBPF in the affected Linux kernel versions. Verifier pruning is essential for analyzing code paths that lead to the execution of a particular eBPF program. However, this vulnerability leads to certain unsafe code paths being marked as safe. Consequently, an attacker can exploit these mislabeled code paths to perform arbitrary read/write operations on the kernel memory, achieve lateral privilege escalation, or even escape containers in containerized environments.

Code Snippet

This code snippet exemplifies how the vulnerability can be exploited using an eBPF program.

struct bpf_insn program[] = {
   // Initialization and setup
   // ...
   BPF_LD_MAP_FD(BPF_REG_1, map_fd),
   BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
   BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -value),
   BPF_STX_MEM(BPF_DW, BPF_REG_, BPF_REG_2, ),
   // ...
   // Triggering arbitrary read/write in kernel memory
   BPF_JMP32_IMM(BPF_JGE, BPF_REG_3, value, label),
   // ...
   // Lateral Privilege Escalation 
};

This code snippet demonstrates the incorrect verifier pruning behavior in affected kernel versions, leading to the kernel believing that the provided eBPF program is safe to execute.

References and Original Reports

1. Joe Security Researcher's Blog Post: In-depth Analysis of CVE-2023-2163
2. Linux Kernel Mailing List: Bug report and discussion about the vulnerability
3. Official CVE details: CVE-2023-2163 - Incorrect verifier pruning in BPF in the Linux kernel

Exploitation Details

It's important to note that this vulnerability requires local access to a target machine. An attacker can then deploy a malicious eBPF program, exploiting the incorrect verifier pruning, which in turn can cause undesirable outcomes like arbitrary kernel memory access, lateral privilege escalation, and container escape.

Conclusion

The vulnerability discussed in this post, CVE-2023-2163, affects Linux kernel versions 5.4 and later due to an implementation flaw in eBPF's verifier component. The consequence is a considerable risk of arbitrary kernel memory read/write operations, lateral privilege escalation, and container escape. It's crucial for system administrators and users who rely on affected kernel versions to stay informed and apply patches or updates as needed.

Timeline

Published on: 09/20/2023 06:15:00 UTC
Last modified on: 09/22/2023 02:02:00 UTC