CVE-2023-35827: Linux Kernel Use-After-Free Vulnerability

CVE-2023-35827 Overview

A use-after-free vulnerability was discovered in the Linux kernel through version 6.3.8. The flaw exists in the ravb_remove function within drivers/net/ethernet/renesas/ravb_main.c, which is part of the Renesas Ethernet AVB (Audio Video Bridging) driver. This vulnerability stems from a race condition that can lead to memory corruption when the driver is being removed.

Critical Impact

Local attackers with low privileges can potentially exploit this use-after-free condition to achieve code execution, escalate privileges, or cause system instability through memory corruption in the Linux kernel.

Affected Products

• Linux Kernel through version 6.3.8
• Systems using Renesas Ethernet AVB hardware with the ravb driver
• Various Linux distributions including Debian (see Debian LTS Announcement)

Discovery Timeline

• 2023-06-18 - CVE-2023-35827 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-35827

Vulnerability Analysis

This vulnerability is classified as a use-after-free (CWE-362 Race Condition) affecting the Linux kernel's Renesas Ethernet AVB driver. The flaw occurs during the driver removal process in the ravb_remove function. When the driver is unloaded, a race condition can occur where memory is freed but subsequently accessed, leading to use-after-free conditions.

The vulnerability requires local access and involves high attack complexity due to the timing-dependent nature of the race condition. An attacker with low privileges on the local system could potentially trigger this condition to corrupt kernel memory, potentially leading to arbitrary code execution with kernel-level privileges or system denial of service.

Root Cause

The root cause is a race condition in the driver removal path. When ravb_remove is called to unload the Renesas Ethernet AVB driver, there is a window where resources are freed but may still be referenced by other code paths. This timing issue allows memory that has been deallocated to be accessed again, resulting in use-after-free behavior. The lack of proper synchronization during the cleanup process creates this exploitable window.

Attack Vector

The attack vector is local, meaning an attacker must have local access to the system to exploit this vulnerability. The exploitation requires:

1. Local system access with low-level privileges
2. Timing manipulation to trigger the race condition during driver removal
3. Presence of Renesas Ethernet AVB hardware or the loaded ravb driver module

The vulnerability can be triggered by initiating driver removal operations while concurrent access to driver resources is occurring. Due to the race condition nature, successful exploitation requires precise timing, making it more difficult to reliably exploit but not impossible for a determined attacker.

The technical details of this vulnerability are documented in the Linux Kernel Mailing List Post and the Netdev Mailing List Message.

Detection Methods for CVE-2023-35827

Indicators of Compromise

• Unexpected kernel crashes or panics related to the ravb driver module
• Memory corruption warnings in kernel logs referencing ravb_main.c or ravb_remove
• Unusual driver load/unload patterns for the Renesas Ethernet AVB module
• Kernel oops messages indicating use-after-free in network driver subsystems

Detection Strategies

• Monitor kernel logs for KASAN (Kernel Address Sanitizer) reports indicating use-after-free in ravb_main.c
• Implement kernel module loading/unloading auditing to detect suspicious driver manipulation
• Deploy SentinelOne Singularity platform for real-time kernel-level threat detection and response
• Use kernel debugging tools to identify race conditions during driver operations

Monitoring Recommendations

• Enable kernel auditing for module operations using auditctl -w /sbin/modprobe -p x
• Configure alerting for kernel panic events and driver-related crashes
• Monitor system stability metrics and track unexpected reboots or crashes
• Review dmesg output regularly for warnings related to the ravb driver

How to Mitigate CVE-2023-35827

Immediate Actions Required

• Update the Linux kernel to a patched version that addresses CVE-2023-35827
• If updates cannot be applied immediately, consider blacklisting the ravb module if the hardware is not in use
• Apply vendor-specific patches from your Linux distribution (see NetApp Security Advisory)
• Restrict local access to the system to trusted users only

Patch Information

The vulnerability has been addressed in Linux kernel updates. Administrators should apply the latest kernel patches from their distribution vendors. The fix involves proper synchronization in the ravb_remove function to prevent the race condition. Debian users should refer to the Debian LTS Announcement for specific package updates. Additional technical details are available in the Netdev Mailing List Message.

Workarounds

• Blacklist the ravb kernel module if Renesas Ethernet AVB hardware is not required: echo "blacklist ravb" >> /etc/modprobe.d/blacklist.conf
• Restrict module loading capabilities to root users only
• Implement SELinux or AppArmor policies to limit driver manipulation
• Consider disabling automatic module loading where possible

# Configuration example - Blacklist the ravb module if not needed
echo "blacklist ravb" | sudo tee /etc/modprobe.d/ravb-blacklist.conf

# Prevent module from being loaded
sudo modprobe -r ravb 2>/dev/null || true

# Verify the module is not loaded
lsmod | grep ravb

# Update initramfs to apply changes on boot
sudo update-initramfs -u