CVE-2026-68188 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: RFCOMM: Fix session UAF in set_termios
rfcomm_tty_set_termios() tests dlc->session without rfcomm_mutex and later passes the pointer to rfcomm_send_rpn(). The latter dereferences both session->initiator and session->sock. Meanwhile, krfcommd can unlink the DLC and free the session while holding rfcomm_mutex.
The race can proceed as follows:
TTY ioctl task krfcommd -------------- -------- load dlc->session enter rfcomm_send_rpn() lock rfcomm_mutex clear dlc->session free session unlock rfcomm_mutex read session->initiator
KASAN reported:
BUG: KASAN: slab-use-after-free in rfcomm_send_rpn+0x297/0x2a0 Read of size 4 at addr ffff88810012a850 by task poc/92
Call Trace: rfcomm_send_rpn+0x297/0x2a0 rfcomm_tty_set_termios+0x50d/0x850 tty_set_termios+0x596/0x950 set_termios+0x46a/0x6e0 tty_mode_ioctl+0x152/0xbd0 tty_ioctl+0x915/0x1240 __x64_sys_ioctl+0x134/0x1c0
Allocated by task 92: rfcomm_session_add+0x9e/0x2e0 rfcomm_dlc_open+0x8b1/0xe00 rfcomm_dev_activate+0x85/0x1a0 rfcomm_tty_open+0x90/0x280
Freed by task 68: kfree+0x131/0x3c0 rfcomm_session_del+0x119/0x180 rfcomm_run+0x737/0x4710
Add rfcomm_dlc_send_rpn(), which holds rfcomm_mutex while it verifies that the DLC is still attached and sends the RPN frame. Have the TTY path use the helper and drop its unlocked session check. This keeps the session valid through both the frame construction and socket send.
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Analysis
by VulDB Data Team • 08/10/2026
This vulnerability represents a use-after-free condition in the Linux kernel's Bluetooth RFCOMM implementation that arises from improper synchronization between concurrent threads accessing shared data structures. The flaw exists in the rfcomm_tty_set_termios function where it reads the dlc->session pointer without holding the rfcomm_mutex lock before passing this pointer to rfcomm_send_rpn. This creates a race condition where another kernel thread can unlink and free the session while the first thread is still processing, leading to memory corruption when the freed memory is subsequently accessed.
The technical execution of this vulnerability demonstrates a classic race condition pattern that aligns with CWE-362, which describes concurrent execution issues leading to security flaws. The specific scenario involves two threads operating in parallel where one thread holds the rfcomm_mutex while freeing memory, and another thread accesses the same freed memory location through the unguarded session pointer. The KASAN report confirms this behavior with a slab-use-after-free error occurring at rfcomm_send_rpn where it attempts to read a 4-byte value from address ffff88810012a850, which was previously freed by kfree during rfcomm_session_del execution.
The operational impact of this vulnerability extends beyond simple memory corruption as it could potentially enable privilege escalation or system instability depending on how the freed memory is reused. Attackers could exploit this condition to execute arbitrary code within kernel space through carefully crafted Bluetooth RFCOMM operations, particularly those involving terminal I/O controls. The vulnerability affects systems running Linux kernels with Bluetooth support and could be triggered through normal Bluetooth TTY device operations, making it particularly dangerous in environments where Bluetooth connectivity is prevalent.
The mitigation strategy implemented involves creating a new helper function rfcomm_dlc_send_rpn that ensures proper locking throughout the entire operation sequence. This approach follows the principle of maintaining atomic access to shared resources by holding the rfcomm_mutex from the point of validation through frame construction and socket transmission. The solution addresses the root cause by eliminating the unlocked session pointer access in the TTY path, thereby ensuring that any session referenced remains valid for the duration of the RPN frame construction and transmission process. This fix aligns with ATT&CK technique T1068 by preventing unauthorized privilege escalation through kernel memory corruption vulnerabilities, and specifically targets the system security weakness identified in CVE-2024-XXXX where improper synchronization leads to exploitable race conditions in kernel subsystems.