CVE-2023-35001 is a critical security vulnerability that affects the Linux Kernel's nftables subsystem. This vulnerability allows an attacker to perform an out-of-bounds read/write exploit. The cause of this issue is the poor handling of vm register contents by the nft_byteorder function when CAP_NET_ADMIN capability is present in any user or network namespace.

In this long read post, we will discuss the root cause of this vulnerability, provide details about the exploit, share a code snippet to aid understanding, and link to original references for further information.

Root Cause Analysis

In the Linux Kernel, nftables is a subsystem that provides packet filtering and classification. It is responsible for managing network rules and access control. The nft_byteorder function within this subsystem is designed to handle byte order conversion of Load Immediate (LDI) register contents.

The issue arises when the nft_byteorder function is called with CAP_NET_ADMIN capability present in any user or network namespace. In this situation, the function poorly handles the vm register contents and can result in out-of-bounds read or write access.

The vulnerability is critical because it allows an attacker to compromise the security of a system in various ways, such as arbitrary code execution or denial of service.

Exploit Details

An attacker with CAP_NET_ADMIN capability can exploit this vulnerability by sending specially crafted network packets to a target system. These packets can be designed to trigger the vulnerable nft_byteorder function and execute arbitrary code on the affected system.

The exploit can be leveraged in two ways – out-of-bounds read and out-of-bounds write

1. Out-of-bounds read: An attacker can read sensitive data from kernel memory, which may contain encryption keys, user credentials, or other sensitive information.
2. Out-of-bounds write: An attacker can write arbitrary data to kernel memory, which can lead to code execution or system crashes, ultimately causing a denial of service.

Here is a simplified code snippet that demonstrates the vulnerability in the nft_byteorder function

void nft_byteorder(const struct nft_ctx *ctx, struct nft_data_desc *desc,
		   struct nft_registers *regs)
{
	uint32_t offset;
	...
	if (!capable(CAP_NET_ADMIN)) {
		// properly handle vm register contents
	}
	else {
		// poor handling of vm register contents
		// allows out-of-bounds read/write
		offset = regs->buffer[desc->len];
		...
		if (offset > MAX_BUFFER_SIZE) {
			// out-of-bounds access
			...
		}
		...
	}
	...
}

As illustrated above, the nft_byteorder function handles the vm register contents differently when the CAP_NET_ADMIN capability is present.

The following sources provide more information on this vulnerability

1. Linux Kernel Source Code - This is the official repository for the Linux Kernel source code.
2. Vulnerability Details in the National Vulnerability Database (NVD) - The NVD provides comprehensive information about the CVE-2023-35001 vulnerability.

Conclusion

CVE-2023-35001 is a significant vulnerability affecting the Linux Kernel's nftables subsystem. This out-of-bounds read/write issue is caused by poor handling of vm register contents by the nft_byteorder function when CAP_NET_ADMIN is present in any user or network namespace.

The exploit allows attackers with the appropriate capability to read sensitive data from kernel memory or write arbitrary data, potentially executing code or causing a denial of service.

It is crucial for system administrators and developers to be aware of this vulnerability and implement appropriate security measures to mitigate its impact on their systems. Regular updates, careful access control, and in-depth knowledge of kernel functions and vulnerabilities can help prevent such issues from becoming a significant security risk.

Timeline

Published on: 07/05/2023 19:15:00 UTC
Last modified on: 08/24/2023 19:15:00 UTC