CVE-2022-43750: Linux Kernel Privilege Escalation Flaw

CVE-2022-43750 Overview

A memory corruption vulnerability exists in the Linux kernel's USB monitor (usbmon) subsystem, specifically in drivers/usb/mon/mon_bin.c. This flaw allows a user-space client to corrupt the monitor's internal memory by exploiting improper memory mapping permissions. The vulnerability affects Linux kernel versions before 5.19.15 and 6.x versions before 6.0.1.

Critical Impact

Local attackers with elevated privileges can corrupt kernel memory through improperly configured memory-mapped regions, potentially leading to privilege escalation, system instability, or arbitrary code execution in kernel context.

Affected Products

• Linux Kernel versions prior to 5.19.15
• Linux Kernel 6.x versions prior to 6.0.1
• Debian Linux 10.0

Discovery Timeline

• 2022-10-26 - CVE-2022-43750 published to NVD
• 2025-05-07 - Last updated in NVD database

Technical Details for CVE-2022-43750

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write) and exists within the USB monitoring subsystem of the Linux kernel. The usbmon driver provides a mechanism for user-space applications to monitor USB traffic for debugging purposes. The flaw stems from the mon_bin_mmap() function in drivers/usb/mon/mon_bin.c, which handles memory mapping of the monitor's internal buffer to user space.

The vulnerability allows user-space processes to obtain writable mappings to the monitor's internal memory structures. When a privileged user-space client memory-maps the usbmon buffer with write permissions, they can corrupt critical kernel data structures used by the monitoring subsystem. This corruption could lead to memory safety violations, denial of service conditions, or potentially enable further exploitation for privilege escalation.

Root Cause

The root cause lies in the failure to enforce read-only permissions on memory-mapped regions in the usbmon driver. Prior to the patch, the mon_bin_mmap() function did not validate or restrict the VM_WRITE flag when user-space applications requested memory mappings. This oversight allowed writable mappings to kernel memory that should have been strictly read-only, violating the intended security model of the USB monitoring interface.

Attack Vector

Exploitation requires local access and elevated privileges. An attacker with appropriate privileges can:

1. Open the usbmon device file (typically /dev/usbmon*)
2. Request a memory mapping with write permissions using mmap() with PROT_WRITE
3. Directly modify the mapped kernel memory regions
4. Corrupt internal data structures used by the USB monitoring subsystem

The attack vector is local, requiring an authenticated user with sufficient privileges to access the usbmon device, which is typically restricted to root or users in specific groups.

 {
 	/* don't do anything here: "fault" will set up page table entries */
 	vma->vm_ops = &mon_bin_vm_ops;

+	if (vma->vm_flags & VM_WRITE)
+		return -EPERM;
+
+	vma->vm_flags &= ~VM_MAYWRITE;
 	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_private_data = filp->private_data;
 	mon_bin_vma_open(vma);

Source: GitHub Linux Commit a659daf63d

The patch adds explicit checks to reject write mappings (VM_WRITE) with -EPERM and clears the VM_MAYWRITE flag to prevent subsequent write permission upgrades.

Detection Methods for CVE-2022-43750

Indicators of Compromise

• Unusual access patterns to /dev/usbmon* device files with write operations
• Kernel log messages indicating memory corruption or unexpected behavior in the usbmon subsystem
• System instability or crashes related to USB monitoring functionality
• Privilege escalation attempts following usbmon device access

Detection Strategies

• Monitor for mmap() system calls targeting usbmon devices with PROT_WRITE flags using auditd or kernel tracing
• Implement file integrity monitoring on kernel modules and usbmon-related kernel objects
• Deploy kernel-level monitoring to detect anomalous memory access patterns in USB subsystem regions
• Use SentinelOne's Linux agent to detect behavioral indicators associated with kernel memory corruption attempts

Monitoring Recommendations

• Enable audit rules for access to /dev/usbmon* devices: auditctl -w /dev/usbmon0 -p rwxa
• Monitor kernel logs for usbmon-related errors or warnings using syslog aggregation
• Implement real-time alerting for privileged processes accessing USB monitoring interfaces
• Deploy endpoint detection solutions capable of monitoring kernel-level activity

How to Mitigate CVE-2022-43750

Immediate Actions Required

• Update Linux kernel to version 5.19.15 or later for the 5.x branch
• Update Linux kernel to version 6.0.1 or later for the 6.x branch
• Restrict access to /dev/usbmon* devices using appropriate file permissions and group membership
• Consider disabling the usbmon module if USB debugging functionality is not required

Patch Information

The vulnerability has been addressed in upstream Linux kernel commits. The fix (commit a659daf63d16aa883be42f3f34ff84235c302198) enforces read-only memory mappings for the usbmon buffer by rejecting write requests and clearing the VM_MAYWRITE flag.

Patch resources:

• Linux Kernel ChangeLog 5.19.15
• Linux Kernel ChangeLog 6.0.1
• Linux Git Commit a659daf63d

For Debian systems, consult the Debian LTS Announcement November 2022 and Debian LTS Announcement December 2022 for distribution-specific updates.

Workarounds

• Disable the usbmon kernel module if not required: modprobe -r usbmon and blacklist in /etc/modprobe.d/
• Restrict device access permissions: chmod 600 /dev/usbmon*
• Limit access to trusted users only through group-based access controls
• Implement mandatory access control policies (SELinux/AppArmor) to restrict usbmon device access

# Configuration example
# Disable usbmon module
echo "blacklist usbmon" >> /etc/modprobe.d/blacklist-usbmon.conf
modprobe -r usbmon

# Restrict device permissions if module must remain loaded
chmod 600 /dev/usbmon*
chown root:root /dev/usbmon*

# Add udev rule for persistent permissions
echo 'KERNEL=="usbmon*", MODE="0600", OWNER="root", GROUP="root"' > /etc/udev/rules.d/99-usbmon-restrict.rules
udevadm control --reload-rules