CVE-2026-68339 Overview
CVE-2026-68339 affects the Linux kernel Bluetooth USB (btusb) driver, specifically the btusb_recv_event_realtek() function. The function reads the event code at data[0] and the Realtek subevent code at data[2] before deciding whether to consume a vendor event as a coredump. Short vendor events that contain only a two-byte header can trigger out-of-bounds reads because the classifier accesses a nonexistent third byte. If the adjacent memory byte happens to be 0x34, the driver misclassifies the event as a coredump. The fix requires the HCI event header and first parameter to be present before inspecting the Realtek subevent code.
Critical Impact
Short Bluetooth vendor events from Realtek adapters can trigger out-of-bounds reads and event misclassification in the Linux kernel btusb driver.
Affected Products
- Linux kernel Bluetooth subsystem (drivers/bluetooth/btusb.c)
- Systems using Realtek Bluetooth USB adapters
- Distributions shipping the vulnerable btusb driver prior to the referenced patches
Discovery Timeline
- 2026-08-10 - CVE-2026-68339 published to NVD
- 2026-08-10 - Last updated in NVD database
Technical Details for CVE-2026-68339
Vulnerability Analysis
The flaw resides in btusb_recv_event_realtek(), which classifies incoming Bluetooth Host Controller Interface (HCI) events from Realtek USB adapters. The function inspects data[0] (the HCI event code) and data[2] (the Realtek subevent code) to determine whether the packet represents a vendor coredump. This lookup occurs without first validating that data[2] lies within the received buffer.
A two-byte event such as ff 00 is a complete vendor event declaring zero parameters. The pre-patch classifier still dereferences a third byte beyond the valid payload. When that adjacent byte holds the value 0x34, the driver treats the short event as a Realtek coredump and routes it into the coredump handler instead of the normal HCI receive path.
Root Cause
The root cause is missing input validation on event length before indexed access into the event buffer, an out-of-bounds read condition. The classifier assumed a minimum payload size without enforcing it. The fix requires the presence of both the HCI event header and the first parameter byte before inspecting the Realtek subevent code. Short events now continue through the normal HCI receive path, which handles their protocol validation.
Attack Vector
Exploitation requires the delivery of a crafted or malformed Bluetooth HCI event from a Realtek USB Bluetooth controller. The attack surface is local to systems with vulnerable Realtek hardware attached. An attacker with control over Bluetooth traffic reaching the host, or a malfunctioning or malicious controller, can cause the driver to read beyond the event payload and misroute packets into the coredump path.
No verified public exploit code is available. See the Linux Kernel patches referenced below for the corrected boundary checks.
Detection Methods for CVE-2026-68339
Indicators of Compromise
- Unexpected Bluetooth coredump events logged by the btusb driver on hosts with Realtek adapters
- Kernel log entries referencing btusb_recv_event_realtek() processing malformed short vendor events
- Anomalous HCI event traffic containing two-byte vendor events with event code 0xff
Detection Strategies
- Audit installed kernel versions against the fixed commits: 24b0758193d7, 400267bab0f4, 8881daaafadb, 8de58bfa26e0, and df541cd485ff
- Monitor dmesg and journalctl -k output for Realtek btusb coredump messages triggered without a preceding fault condition
- Inventory endpoints with Realtek Bluetooth USB hardware and correlate against kernel patch level
Monitoring Recommendations
- Enable kernel address sanitizer (KASAN) in test environments to catch out-of-bounds reads in drivers/bluetooth/btusb.c
- Track Bluetooth subsystem crash and coredump frequency as a baseline anomaly signal
- Alert on hosts running kernels older than the patched revisions where Realtek Bluetooth interfaces are active
How to Mitigate CVE-2026-68339
Immediate Actions Required
- Apply the upstream Linux kernel patches referenced by commits 24b0758193d7, 400267bab0f4, 8881daaafadb, 8de58bfa26e0, and df541cd485ff
- Update to a distribution kernel that incorporates the fix for btusb_recv_event_realtek()
- Prioritize patching on laptops, workstations, and IoT devices shipping Realtek Bluetooth chipsets
Patch Information
The fix is available in the upstream Linux kernel through the following stable commits: 24b0758193d7, 400267bab0f4, 8881daaafadb, 8de58bfa26e0, and df541cd485ff. The patches require the HCI event header and first parameter to be present before inspecting the Realtek subevent code.
Workarounds
- Unload the btusb kernel module on hosts that do not require Bluetooth: modprobe -r btusb
- Physically disconnect or disable Realtek Bluetooth USB adapters on systems that cannot be patched immediately
- Blocklist the btusb module via /etc/modprobe.d/ on endpoints where Bluetooth is not operationally required
# Configuration example
# Blocklist btusb until kernel is patched
echo "blacklist btusb" | sudo tee /etc/modprobe.d/blacklist-btusb.conf
sudo modprobe -r btusb
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
