CVE-2026-68188 Overview
CVE-2026-68188 is a use-after-free (UAF) vulnerability in the Linux kernel's Bluetooth RFCOMM subsystem. The flaw exists in rfcomm_tty_set_termios(), which reads dlc->session without acquiring rfcomm_mutex and later passes the pointer to rfcomm_send_rpn(). The krfcommd thread can concurrently unlink the DLC and free the session, causing a stale pointer dereference. KASAN identified the issue as a slab-use-after-free on session->initiator. The fix introduces rfcomm_dlc_send_rpn(), which holds rfcomm_mutex while validating that the DLC remains attached before transmitting the RPN frame.
Critical Impact
A local attacker with access to Bluetooth RFCOMM TTY devices can trigger a race condition that dereferences freed kernel memory, resulting in denial of service or potential local privilege escalation.
Affected Products
- Linux kernel — Bluetooth RFCOMM subsystem
- Distributions shipping the vulnerable RFCOMM code prior to the upstream fix
- Systems exposing /dev/rfcomm* TTY devices to unprivileged users
Discovery Timeline
- 2026-08-10 - CVE-2026-68188 published to NVD
- 2026-08-10 - Last updated in NVD database
Technical Details for CVE-2026-68188
Vulnerability Analysis
The vulnerability is a use-after-free triggered by a race between the TTY ioctl path and the krfcommd kernel thread. When userspace invokes TCSETS or a related termios ioctl on an RFCOMM TTY, control reaches rfcomm_tty_set_termios(). This function reads dlc->session without any locking, then calls rfcomm_send_rpn(), which dereferences session->initiator and session->sock.
Concurrently, krfcommd acquires rfcomm_mutex, clears dlc->session, frees the session via rfcomm_session_del(), and releases the mutex. If the ioctl task loaded the pointer before the free but dereferences it after, the kernel reads freed slab memory. KASAN confirmed the pattern with a slab-use-after-free report at rfcomm_send_rpn+0x297/0x2a0.
The root problem is that lifetime management of the RFCOMM session relies on rfcomm_mutex, but the TTY set_termios path did not participate in that locking discipline.
Root Cause
The root cause is missing synchronization between session teardown in krfcommd and the RFCOMM TTY termios handler. rfcomm_tty_set_termios() used an unlocked read of dlc->session and forwarded the pointer to code that dereferences session fields, while rfcomm_run() was free to call rfcomm_session_del() and kfree() on the same object under rfcomm_mutex.
Attack Vector
Exploitation requires local access to an RFCOMM TTY device and the ability to issue termios ioctls. An attacker races repeated ioctl(TCSETS) calls against session teardown events. Successful exploitation reads freed kernel memory, which can be shaped into a controlled slab reuse for information disclosure or, with additional heap grooming, kernel memory corruption leading to privilege escalation. Because RFCOMM depends on Bluetooth availability, the attack surface is limited to hosts with active Bluetooth stacks and accessible RFCOMM devices.
No public proof-of-concept code has been released. The KASAN trace embedded in the upstream commit provides sufficient detail for reproduction; see the Linux Kernel Commit Fix for the corrective patch.
Detection Methods for CVE-2026-68188
Indicators of Compromise
- KASAN reports referencing rfcomm_send_rpn, rfcomm_tty_set_termios, or rfcomm_session_del in dmesg or the kernel ring buffer.
- Unexpected kernel oops or panic entries mentioning RFCOMM call paths on systems with active Bluetooth.
- Unprivileged processes repeatedly issuing termios ioctls against /dev/rfcomm* devices.
Detection Strategies
- Enable CONFIG_KASAN on test kernels and monitor for slab-use-after-free reports in the RFCOMM path.
- Audit running kernel versions against distribution advisories referencing the fix commits a82a9d38, 2894bd8c, 780b04d0, 98bc6819, and c783399e.
- Correlate Bluetooth subsystem crashes with concurrent RFCOMM TTY activity using kernel telemetry.
Monitoring Recommendations
- Ship kernel logs to a centralized store and alert on BUG: KASAN, general protection fault, or Oops entries containing rfcomm_.
- Track ioctl syscall telemetry for uids interacting with /dev/rfcomm* device nodes.
- Monitor Bluetooth daemon restarts and RFCOMM DLC churn as potential signs of racing exploitation attempts.
How to Mitigate CVE-2026-68188
Immediate Actions Required
- Apply the upstream Linux kernel patch that introduces rfcomm_dlc_send_rpn() and takes rfcomm_mutex around the DLC validity check and RPN transmission.
- Update to the distribution kernel package that incorporates the fix once released by your vendor.
- Restrict access to /dev/rfcomm* devices to trusted users and services only.
Patch Information
The fix is available upstream in the stable tree. Relevant commits include Linux Kernel Commit Fix, Linux Kernel Commit Summary, Linux Kernel Commit Update, Linux Kernel Commit Changes, and Linux Kernel Commit Modification. The patch adds a helper that holds rfcomm_mutex while confirming the DLC is still attached and sending the RPN frame, eliminating the unlocked pointer read in the TTY path.
Workarounds
- Disable the Bluetooth stack on systems that do not require it by masking bluetooth.service and unloading the bluetooth and rfcomm modules.
- Blacklist the rfcomm kernel module where RFCOMM functionality is unnecessary.
- Tighten permissions on /dev/rfcomm* nodes so only privileged services can invoke termios ioctls.
# Configuration example: disable RFCOMM on systems that do not need it
echo "blacklist rfcomm" | sudo tee /etc/modprobe.d/disable-rfcomm.conf
sudo rmmod rfcomm 2>/dev/null || true
sudo systemctl mask bluetooth.service
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
