CVE-2026-23395: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-23395 is a buffer overflow vulnerability in the Linux kernel's Bluetooth L2CAP (Logical Link Control and Adaptation Protocol) implementation, specifically in the handling of Enhanced Credit Based (ECRED) connection requests. The flaw allows multiple L2CAP_ECRED_CONN_REQ messages with the same command identifier to be accepted and marked as pending (FLAG_DEFER_SETUP), causing more than the maximum allowed L2CAP_ECRED_MAX_CID (5) channel IDs to be allocated in l2cap_ecred_rsp_defer, resulting in a buffer overflow. Affected Linux kernel versions include 5.7 through 5.10.252, 5.11 through 5.15.202, 5.16 through 6.1.166, 6.2 through 6.6.129, 6.7 through 6.12.77, 6.13 through 6.18.19, and 6.19 through 6.19.9, as well as Linux kernel 7.0 release candidates prior to rc5. It carries a CVSS v3.1 base score of 8.8 (High) (Red Hat CVE, Feedly).

The root cause is classified as CWE-1288 (Improper Validation of Consistency within Input). The Bluetooth L2CAP specification mandates that each successive request on a signaling channel must use a different command identifier; however, the vulnerable kernel code fails to enforce this constraint, accepting multiple L2CAP_ECRED_CONN_REQ requests sharing the same identifier. Each accepted request is flagged as FLAG_DEFER_SETUP, and when l2cap_ecred_rsp_defer processes these deferred responses, it can allocate more than the five channel IDs (L2CAP_ECRED_MAX_CID) permitted, triggering a heap buffer overflow. The attack vector is adjacent network (Bluetooth range), requires no privileges and no user interaction, and the fix adds a check to reject any incoming ECRED connection request whose command identifier matches an already-pending channel (Red Hat CVE, Feedly).

Successful exploitation can result in kernel memory corruption, leading to system crashes (denial of service), disclosure of sensitive kernel memory contents, or potentially arbitrary code execution with kernel-level privileges. Because the attack operates at the Bluetooth layer with no authentication or user interaction required, any device with Bluetooth enabled and within radio range is at risk. The full confidentiality, integrity, and availability impact is rated High in each dimension (Red Hat CVE, Feedly).

1. Reconnaissance: Identify target devices with Bluetooth enabled and running a vulnerable Linux kernel version (5.7–6.19.9 or 7.0-rc1 through rc4) within Bluetooth radio range using tools such as hcitool scan or bluetoothctl.
2. Establish Bluetooth proximity: Position within Bluetooth range of the target device (typically up to ~10–100 meters depending on class).
3. Initiate L2CAP signaling: Use a custom Bluetooth stack or raw HCI socket (e.g., via BlueZ's l2ping or a custom Python script using socket.AF_BLUETOOTH) to open an L2CAP signaling channel to the target.
4. Send duplicate-identifier ECRED requests: Craft and transmit multiple L2CAP_ECRED_CONN_REQ packets that share the same command identifier value, bypassing the missing validation check in the vulnerable kernel.
5. Trigger overflow: Each duplicate request is accepted and marked FLAG_DEFER_SETUP; when the kernel processes deferred responses via l2cap_ecred_rsp_defer, more than five channel IDs are allocated, overflowing the buffer and corrupting adjacent kernel memory.
6. Achieve objective: Depending on memory layout and kernel hardening, the attacker may cause a kernel panic (DoS), leak kernel memory, or achieve kernel-level code execution (Red Hat CVE, Feedly).

• Network/Bluetooth: Unusual or repeated L2CAP ECRED connection requests (L2CAP_ECRED_CONN_REQ) from the same Bluetooth device address with identical command identifiers; unexpected Bluetooth pairing or connection attempts from unknown devices.
• Logs: Kernel logs (dmesg, /var/log/kern.log) showing Bluetooth subsystem errors, stack traces, or kernel panics referencing l2cap_ecred_rsp_defer or related L2CAP functions; kernel BUG or OOPS messages in the Bluetooth stack.
• Process/System: Unexpected system reboots or kernel panics on systems with Bluetooth enabled; unusual kernel crash dumps (/var/crash) correlating with Bluetooth activity.
• File System: Presence of kernel crash dump files generated around the time of suspicious Bluetooth activity.

Patches are available across multiple stable kernel branches. Users should upgrade to the following fixed versions or later: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10, or 7.0-rc5. Microsoft Azure Linux kernel 6.6.126.1-1 also contains the fix. Debian, SUSE, and openSUSE have issued updated packages incorporating these fixes. As a temporary workaround for systems that cannot be immediately patched, disable Bluetooth entirely (rfkill block bluetooth) or restrict Bluetooth access at the network boundary to prevent untrusted adjacent-network attackers from sending crafted L2CAP packets (Red Hat CVE, SUSE Advisory, Feedly).

Red Hat published a CVE advisory and Bugzilla entry tracking the issue, rating it High severity. SUSE issued security update announcements (SUSE-SU-2026:2217-1 and SUSE-SU-2026:2238-1) for affected kernel packages. Debian accepted the fix into unstable, stable-security, and backports branches. The Yocto Project security mailing list also discussed the vulnerability across multiple messages. Social media activity was limited to automated CVE tracking accounts (Red Hat CVE, SUSE Advisory).