CVE-2026-23307: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-23307 Overview

CVE-2026-23307 is a buffer overflow vulnerability in the Linux kernel's EMS USB CAN (Controller Area Network) driver. The vulnerability exists in the ems_usb_read_bulk_callback() function, where improper length validation of USB URB (USB Request Block) messages can lead to out-of-bounds memory access. When parsing bulk transfer data, the driver incorrectly relies on transfer_buffer_length (the maximum buffer size set by the driver) instead of actual_length (the actual size of data received), which can result in buffer overflow conditions when processing malformed or malicious USB messages.

Critical Impact

Attackers with physical USB access or through compromised USB devices could potentially exploit this vulnerability to cause kernel crashes, denial of service, or potentially achieve local privilege escalation through memory corruption.

Affected Products

• Linux Kernel (versions with vulnerable ems_usb CAN driver)
• Systems using EMS CPC-USB/ARM7 CAN interface adapters
• Industrial control systems and automotive applications utilizing CAN bus over USB

Discovery Timeline

• 2026-03-25 - CVE CVE-2026-23307 published to NVD
• 2026-03-25 - Last updated in NVD database

Technical Details for CVE-2026-23307

Vulnerability Analysis

The vulnerability resides in the ems_usb_read_bulk_callback() function within the EMS USB CAN driver (drivers/net/can/usb/ems_usb.c). This callback function processes incoming bulk transfer data from EMS CPC-USB CAN adapters. The core issue stems from a failure to properly validate message boundaries when parsing multiple CAN messages from a single USB bulk transfer.

USB bulk transfers can contain multiple CAN messages packed together. The driver must iterate through these messages, parsing each one according to its declared length. However, the original implementation failed to perform adequate bounds checking in two critical areas:

1. At message start: The code did not verify that the remaining buffer contained enough bytes for the expected message structure header before attempting to read message fields.

2. At message end: After processing a message, the code did not confirm that the calculated next message offset remained within the valid actual_length boundary, potentially causing reads past the end of the received data.

Root Cause

The root cause is improper input validation in the USB bulk callback handler. The driver confused two distinct concepts: transfer_buffer_length represents the maximum allocated buffer size, while actual_length represents the actual number of bytes received in the current transfer. By failing to use actual_length as the authoritative boundary for parsing operations, the driver could read beyond valid data into uninitialized or adjacent memory regions.

This represents a classic boundary condition error where untrusted input (the USB data length and message structures) was processed without sufficient validation against the actual data received.

Attack Vector

An attacker could exploit this vulnerability through physical access to the USB port by connecting a malicious USB device that emulates an EMS CAN adapter. The malicious device could send crafted bulk transfer responses with:

• Invalid message length fields that point beyond the actual received data
• Truncated messages that cause the parser to read past buffer boundaries
• Multiple messages where the cumulative size exceeds actual_length

Since the vulnerability is in the USB driver layer, exploitation requires either physical access to plug in a malicious device or compromise of an existing connected EMS CAN adapter. In industrial or automotive environments where CAN bus interfaces are deployed, this could represent a significant attack surface.

Detection Methods for CVE-2026-23307

Indicators of Compromise

• Kernel panic or oops messages referencing ems_usb_read_bulk_callback or the ems_usb module
• Unexpected system crashes or reboots on systems with EMS USB CAN adapters connected
• Kernel log entries showing memory corruption or invalid memory access in USB subsystem contexts
• Unusual USB device connection events followed by kernel stability issues

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for stack traces involving ems_usb driver functions
• Implement kernel module integrity monitoring to detect tampering with CAN driver modules
• Deploy USB device whitelisting to restrict unknown or unauthorized CAN adapters from connecting
• Use kernel address sanitizer (KASAN) in test environments to detect out-of-bounds memory accesses

Monitoring Recommendations

• Enable kernel crash dump collection (kdump) to capture forensic data from exploitation attempts
• Implement USB device auditing through udev rules to log all CAN adapter connections
• Monitor for anomalous USB traffic patterns using hardware USB analyzers in sensitive environments
• Review system stability logs for patterns of crashes correlating with USB device activity

How to Mitigate CVE-2026-23307

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the security fix for the ems_usb driver
• Restrict physical access to USB ports on systems with sensitive CAN bus interfaces
• Consider disabling the ems_usb kernel module if EMS CAN adapters are not required in your environment
• Implement USB device authorization policies to prevent unauthorized device connections

Patch Information

The Linux kernel maintainers have released patches addressing this vulnerability. The fix adds proper length validation at both the beginning of message parsing (to ensure sufficient space for the message structure) and at the end of each message (to prevent overflow when advancing to the next message).

Multiple stable kernel branches have received patches:

• Kernel Security Patch 1818974
• Kernel Security Patch 18f75b9
• Kernel Security Patch 1cf4690
• Kernel Security Patch 2833e13
• Kernel Security Patch 38a01c9
• Kernel Security Patch c703bbf

Workarounds

• Blacklist the ems_usb kernel module by adding blacklist ems_usb to /etc/modprobe.d/blacklist.conf if the driver is not needed
• Use USB port blocking hardware or software to prevent unauthorized USB device connections
• Implement network segmentation to isolate systems with CAN bus interfaces from general network access
• Deploy host-based intrusion detection to monitor for kernel-level exploitation attempts

# Disable ems_usb module if not required
echo "blacklist ems_usb" | sudo tee /etc/modprobe.d/blacklist-ems_usb.conf
sudo update-initramfs -u

# Unload the module if currently loaded
sudo modprobe -r ems_usb

# Verify module is not loaded
lsmod | grep ems_usb