CVE-2023-35828: Linux Kernel Use-After-Free Vulnerability

CVE-2023-35828 Overview

A use-after-free vulnerability was discovered in the Linux kernel before version 6.3.2. The vulnerability exists in the renesas_usb3_remove function within drivers/usb/gadget/udc/renesas_usb3.c. This memory corruption issue can be triggered through a race condition during the USB device removal process, potentially allowing a local attacker with low privileges to achieve code execution or cause system instability.

Critical Impact

Local attackers with low privileges can exploit this use-after-free vulnerability to potentially execute arbitrary code with elevated privileges or cause system crashes, compromising system integrity, confidentiality, and availability.

Affected Products

• Linux Kernel (versions before 6.3.2)
• NetApp H300S
• NetApp H410C
• NetApp H410S
• NetApp H500S
• NetApp H700S

Discovery Timeline

• 2023-06-18 - CVE-2023-35828 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-35828

Vulnerability Analysis

This vulnerability is a use-after-free condition caused by a race condition (CWE-362) in the Renesas USB3 gadget driver. The flaw occurs in the renesas_usb3_remove function, which handles the cleanup process when a Renesas USB3 device is removed from the system. Due to improper synchronization, there exists a timing window where memory that has been freed can still be accessed by concurrent operations.

The vulnerability requires local access and involves high attack complexity due to the race condition nature of the exploit. An attacker must win a race between the device removal path and other concurrent USB operations. Despite the complexity, successful exploitation can lead to complete compromise of system confidentiality, integrity, and availability.

Root Cause

The root cause lies in insufficient synchronization mechanisms within the renesas_usb3_remove function. When a Renesas USB3 device is being removed, the driver deallocates memory structures associated with the device. However, a race condition exists where other kernel threads or interrupt handlers may still hold references to these structures and attempt to access them after deallocation. This time-of-check to time-of-use (TOCTOU) vulnerability allows the freed memory to be accessed, leading to a use-after-free condition.

Attack Vector

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

1. The attacker initiates or waits for a Renesas USB3 device removal event
2. A race condition is triggered during the renesas_usb3_remove execution
3. The attacker exploits the timing window to access freed memory structures
4. Successful exploitation can lead to arbitrary code execution in kernel context or system crash

The vulnerability manifests in the device removal handling code path within the Renesas USB3 driver. The specific technical details and the fix can be found in the Linux Kernel Commit Update which addresses the race condition by implementing proper synchronization during device removal.

Detection Methods for CVE-2023-35828

Indicators of Compromise

• Unexpected kernel panics or system crashes during USB device removal operations
• Suspicious memory corruption errors in kernel logs related to the Renesas USB3 driver
• Abnormal behavior when unplugging USB devices on systems with Renesas USB3 controllers
• Kernel oops messages referencing renesas_usb3_remove or related functions

Detection Strategies

• Monitor kernel logs (dmesg) for use-after-free warnings or memory corruption errors involving the renesas_usb3 driver module
• Implement kernel address sanitizer (KASAN) in test environments to detect use-after-free conditions
• Use SentinelOne Singularity platform to monitor for suspicious kernel-level activities and memory anomalies
• Deploy endpoint detection rules that alert on unexpected USB driver behavior patterns

Monitoring Recommendations

• Enable enhanced kernel logging to capture detailed driver operations during USB device events
• Configure SentinelOne agents to monitor for kernel exploit attempts and memory corruption indicators
• Regularly review system stability logs for patterns consistent with race condition exploitation
• Implement runtime kernel integrity monitoring to detect unauthorized kernel memory modifications

How to Mitigate CVE-2023-35828

Immediate Actions Required

• Update the Linux kernel to version 6.3.2 or later immediately on all affected systems
• For NetApp appliances (H300S, H410C, H410S, H500S, H700S), apply the vendor patches referenced in NetApp Security Advisory NTAP-20230803-0002
• If immediate patching is not possible, consider disabling or unloading the renesas_usb3 module on systems where Renesas USB3 controllers are not required
• Restrict local access to systems to trusted users only until patches can be applied

Patch Information

The vulnerability is fixed in Linux kernel version 6.3.2. The specific patch can be reviewed in the Linux Kernel ChangeLog 6.3.2. The fix addresses the race condition by implementing proper synchronization during the device removal process in the Renesas USB3 driver.

For Debian-based systems, refer to the Debian LTS Advisory Announcement for distribution-specific patch information.

Technical discussion of the fix can be found in the Kernel Mailing List Discussion.

Workarounds

• Unload the renesas_usb3 module using modprobe -r renesas_usb3 if the Renesas USB3 controller functionality is not required
• Blacklist the driver by adding blacklist renesas_usb3 to /etc/modprobe.d/blacklist.conf to prevent automatic loading
• Limit physical access to USB ports on affected systems to reduce the attack surface
• Implement kernel module loading restrictions using security modules like SELinux or AppArmor

# Workaround: Blacklist the vulnerable driver module
echo "blacklist renesas_usb3" >> /etc/modprobe.d/blacklist-renesas.conf

# Unload the module if currently loaded
modprobe -r renesas_usb3

# Verify the module is not loaded
lsmod | grep renesas_usb3