CVE-2023-1032: Linux Kernel Use-After-Free Vulnerability

CVE-2023-1032 Overview

CVE-2023-1032 is a double free vulnerability affecting the Linux kernel's io_uring subsystem. The flaw exists in the IORING_OP_SOCKET operation within the __sys_socket_file() function located in net/socket.c. This memory corruption vulnerability allows a local attacker with low privileges to cause a denial of service condition by triggering a system crash.

Critical Impact

Local attackers can exploit this double free condition to crash the system, resulting in denial of service. The vulnerability affects systems running vulnerable Linux kernel versions with io_uring enabled.

Affected Products

• Linux Kernel (versions between commits da214a475f8bd1d3e9e7a19ddfeb4d1617551bab and 649c15c7691e9b13cbe9bf6c65c365350e056067)
• Linux Kernel 6.3-rc1
• Canonical Ubuntu Linux 22.04 LTS
• Canonical Ubuntu Linux 22.10

Discovery Timeline

• January 8, 2024 - CVE CVE-2023-1032 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-1032

Vulnerability Analysis

This vulnerability is classified as CWE-415 (Double Free), a memory corruption flaw where the same memory allocation is freed twice. In the context of the Linux kernel's io_uring subsystem, this occurs during the IORING_OP_SOCKET operation when handling socket file creation.

The io_uring interface is designed to provide efficient asynchronous I/O operations in the Linux kernel. The IORING_OP_SOCKET operation allows userspace applications to create sockets through the io_uring submission queue. When this operation is processed, the __sys_socket_file() function in net/socket.c is invoked to handle the socket file descriptor creation.

The double free condition arises from improper error handling paths in the socket creation code. When certain error conditions occur, the code may attempt to free the same memory region twice, leading to heap corruption. This corruption can cause kernel panics or system crashes when the memory allocator encounters the corrupted heap state.

Root Cause

The root cause of this vulnerability is improper memory management in the error handling path of the __sys_socket_file() function. The issue was introduced in commit da214a475f8bd1d3e9e7a19ddfeb4d1617551bab which added the IORING_OP_SOCKET functionality. The code failed to properly track whether memory had already been freed during error cleanup, resulting in the potential for double free conditions when specific error paths were triggered.

Attack Vector

The attack requires local access to the system with low privileges. An attacker must be able to interact with the io_uring interface, which is available to unprivileged users by default on many Linux distributions. The attacker can craft malicious io_uring submission queue entries that trigger the vulnerable code path, causing the double free condition and resulting in a kernel crash.

The exploitation mechanism involves submitting specially crafted IORING_OP_SOCKET requests through the io_uring interface that trigger the error handling path containing the double free. Since no user interaction is required and the attack complexity is low, exploitation is straightforward for attackers with local access.

Detection Methods for CVE-2023-1032

Indicators of Compromise

• Unexpected kernel panics or system crashes related to memory corruption in the io_uring subsystem
• Kernel log messages indicating double free or heap corruption in net/socket.c or io_uring components
• Unusual io_uring activity patterns from unprivileged processes
• System instability following io_uring socket operations

Detection Strategies

• Monitor kernel logs for memory corruption warnings, particularly those referencing __sys_socket_file() or io_uring operations
• Implement kernel auditing to track io_uring syscall usage and flag anomalous patterns
• Deploy endpoint detection solutions capable of identifying exploitation attempts targeting kernel memory corruption vulnerabilities
• Use kernel debugging tools like KASAN (Kernel Address Sanitizer) in development environments to detect double free conditions

Monitoring Recommendations

• Enable and review kernel crash dumps (kdump) to identify potential exploitation attempts
• Monitor for processes making excessive io_uring submissions, particularly IORING_OP_SOCKET operations
• Implement system call auditing focused on io_uring_setup and io_uring_enter syscalls
• Deploy SentinelOne's Singularity platform for real-time kernel-level threat detection and response

How to Mitigate CVE-2023-1032

Immediate Actions Required

• Update the Linux kernel to a version containing the fix (commit 649c15c7691e9b13cbe9bf6c65c365350e056067 or later)
• Apply distribution-specific patches from Ubuntu (USN-5977-1, USN-6024-1, USN-6033-1) or other vendors
• Consider temporarily disabling io_uring on critical systems if immediate patching is not possible
• Audit systems for signs of exploitation attempts before and after patching

Patch Information

The vulnerability has been fixed in commit 649c15c7691e9b13cbe9bf6c65c365350e056067. Ubuntu has released security updates addressing this issue through multiple security notices:

• Ubuntu Security Notice USN-5977-1
• Ubuntu Security Notice USN-6024-1
• Ubuntu Security Notice USN-6033-1

Additional technical details are available through the Openwall OSS Security Discussion.

Workarounds

• Disable io_uring system-wide using kernel parameters or sysctl settings if patching is not immediately possible
• Restrict io_uring access using seccomp filters for untrusted or unnecessary applications
• Implement container security policies to limit io_uring access within containerized environments
• Use kernel hardening techniques such as enabling SLAB/SLUB hardening options

# Disable io_uring system-wide (temporary workaround)
echo 0 > /proc/sys/kernel/io_uring_disabled

# Or via sysctl for persistence across reboots
echo "kernel.io_uring_disabled = 2" >> /etc/sysctl.conf
sysctl -p