# CVE-2026-72336: Bluetooth: 6lowpan: hold L2CAP conn across debugfs control > A use-after-free in the Linux kernel Bluetooth 6LoWPAN module allows local attackers to execute code or escalate privileges via debugfs. - **Severity:** Not scored - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 15 Aug 2026 - **Updated:** 17 Aug 2026 - **Also known as:** BELL-CVE-2026-72336, DEBIAN-CVE-2026-72336, GHSA-53r8-c46r-w2fg, UBUNTU-CVE-2026-72336 ## What is CVE-2026-72336? CVE-2026-72336 is an use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description In the Linux kernel, the following vulnerability has been resolved: Bluetooth: 6lowpan: hold L2CAP conn across debugfs control get_l2cap_conn() looks up an LE hci_conn under hdev protection, but then drops that protection before reading hcon->l2cap_data and before lowpan_control_write() later dereferences conn->hcon. A disconnect or device close can tear down the same L2CAP connection in that window. The buggy scenario involves two paths, with each column showing the order within that path: 6LoWPAN control write: HCI disconnect/device close: 1. get_l2cap_conn() finds hcon 1. hci_disconn_cfm() dispatches and hcon->l2cap_data. the L2CAP disconnect callback. 2. get_l2cap_conn() drops hdev 2. l2cap_conn_del() clears protection and returns conn. hcon->l2cap_data and drops the L2CAP connection reference. 3. lowpan_control_write() reads 3. hci_conn_del() removes and drops conn->hcon. the HCI connection. Take a reference to the L2CAP connection with l2cap_conn_hold_unless_zero() while hdev is still locked, and drop that reference after the debugfs command's last use of conn. This mirrors the existing L2CAP ACL receive-side handoff and keeps the connection dereferenceable after leaving hdev protection. Export the existing helper so the bluetooth_6lowpan module can use the same lifetime primitive. Validation reproduced this kernel report: BUG: KASAN: slab-use-after-free in lowpan_control_write+0x374/0x520 The buggy address belongs to the object at ffff888111b9d000 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 0 bytes inside of freed 1024-byte region [ffff888111b9d000, ffff888111b9d400) Read of size 8 Call trace: dump_stack_lvl+0x66/0xa0 print_report+0xce/0x5f0 lowpan_control_write+0x374/0x520 (net/bluetooth/6lowpan.c:1131) srso_alias_return_thunk+0x5/0xfbef5 __virt_addr_valid+0x19f/0x330 kasan_report+0xe0/0x110 __debugfs_file_get+0xf7/0x400 full_proxy_write+0x9e/0xd0 vfs_write+0x1b0/0x810 ksys_write+0xd2/0x170 dnotify_flush+0x32/0x220 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f Allocated by task stack: kasan_save_stack+0x33/0x60 kasan_save_track+0x17/0x60 __kasan_kmalloc+0xaa/0xb0 l2cap_conn_add+0x45/0x520 l2cap_chan_connect+0xac6/0xd90 l2cap_sock_connect+0x216/0x350 __sys_connect+0x101/0x130 __x64_sys_connect+0x40/0x50 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task stack: kasan_save_stack+0x33/0x60 kasan_save_track+0x17/0x60 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x5f/0x80 kfree+0x313/0x590 hci_conn_hash_flush+0xc0/0x140 hci_dev_close_sync+0x41a/0xb00 hci_dev_close+0x12f/0x160 hci_sock_ioctl+0x157/0x570 sock_do_ioctl+0xf7/0x210 sock_ioctl+0x32f/0x490 __x64_sys_ioctl+0xc7/0x110 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f kasan_record_aux_stack+0xa7/0xc0 insert_work+0x32/0x100 __queue_work+0x262/0xa60 queue_work_on+0xad/0xb0 l2cap_connect_cfm+0x4ef/0x670 hci_le_remote_feat_complete_evt+0x247/0x430 hci_event_packet+0x360/0x6f0 hci_rx_work+0x2ae/0x7a0 process_one_work+0x4fd/0xbc0 worker_thread+0x2d8/0x570 kthread+0x1ad/0x1f0 ret_from_fork+0x3c9/0x540 ret_from_fork_asm+0x1a/0x30 ## Which versions are affected by CVE-2026-72336? ## How do I fix CVE-2026-72336? Apply the vendor's patch. ## Is CVE-2026-72336 being exploited? There is no known exploitation of CVE-2026-72336 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-72336 and fix it if it is affected. What it is: CVE-2026-72336 is an use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-72336 in the wild and no public exploit code. Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-72336/ (Markdown: https://insights.sbomify.com/CVE-2026-72336/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72336 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72336 - OSV: https://osv.dev/vulnerability/CVE-2026-72336 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-72336/ Summaries are generated and may contain mistakes; the official description above is the record.