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CVE-2026-90091
Bluetooth: L2CAP: fix race l2cap_sock_cleanup_listen() vs. put_chan
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-90091 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
For L2CAP sockets without owning sk->sk_socket, reading l2cap_pi(sk)->chan may race against concurrent l2cap_sock_kill() -> l2cap_sock_put_chan(). This excludes simultaneous proto_ops callbacks, but access in l2cap_sock_cleanup_listen() has unsafe lockless read. [Task 1] [Task 2 (hdev->workqueue)] l2cap_sock_release(parent) l2cap_disconn_cfm l2cap_sock_cleanup_listen l2cap_conn_del bt_accept_dequeue l2cap_chan_del lock_sock(sk) l2cap_sock_teardown_cb bt_accept_unlink bt_sk(sk)->parent = NULL release_sock(sk) ----------------> lock_sock(sk) parent = /* NULL */ lock_sock(sk) <--------------------- release_sock(sk) sock_set_flag(sk, SOCK_ZAPPED) l2cap_sock_close_cb l2cap_sock_kill(sk) l2cap_sock_put_chan chan = READ l2cap_pi(sk)->chan l2cap_pi(sk)->chan = NULL l2cap_chan_hold_unless_zero l2cap_put_chan(chan) kref_get_unless_zero(&chan->ref) Task 1 may observe NULL which causes null-ptr-deref. Fix the race by taking lock_sock() in l2cap_sock_kill() to synchronize with l2cap_sock_cleanup_listen(). hold_unless_zero() is not needed here, l2cap_pi(sk)->chan owns reference if it is non-NULL. Clarify code comments vs. locking.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
include/net/bluetooth/l2cap.h
net/bluetooth/l2cap_sock.c
- What this is
- BLUETOOTH SUBSYSTEMMAINTAINERS section matched on include/net/bluetooth/ · linux-bluetooth@vger.kernel.org · Supported
- Kernel module
- bluetooth
Check it on the machine
grep -w CONFIG_BT /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w bluetoothPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x
- bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_BT
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-17 (31 days ago)source
- CVSS
- 8.0 high
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- adjacent network (AV:A)source
- EPSS
- 0.35%, higher than 27.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.1.178 | 6.1.188 | 827de6bd2865 |
| 6.6.145 | 6.6.157 | 7c7ac736b50f |
| 6.12.97 | 6.12.110 | 4f8c63fe0097 |
| 6.18.40 | 6.18.52 | 61d5ddbd524c |
| 7.2 | 7.2.6 | 32a7bc6e93be |
| 7.2 | 7.3 | 66d6ef18548a |
| 7.1.5 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:AAttack vector, adjacent network
- A nearby peer's HCI Disconnection Complete (hci_disconn_complete_evt → hci_disconn_cfm → l2cap_disconn_cfm on hdev->rx_work) or L2CAP_DISCONN_REQ (l2cap_disconnect_req) runs l2cap_sock_put_chan on an unaccepted child created by L2CAP_CONN_REQ; the transport is Bluetooth radio range, so Adjacent not Network.
- AC:LAttack complexity, low
- The attacker drives both sides: close() of their listening socket runs l2cap_sock_release → l2cap_sock_cleanup_listen → bt_accept_dequeue, while the peer's disconnect concurrently runs l2cap_sock_kill → l2cap_sock_put_chan on that child without lock_sock; repeating connect/disconnect/close hits the window.
- PR:LPrivileges required, low
- l2cap_sock_create() allows unprivileged SOCK_SEQPACKET/SOCK_STREAM (only SOCK_RAW needs CAP_NET_RAW), and l2cap_validate_bredr_psm() permits dynamic PSM >= 0x1001 without CAP_NET_BIND_SERVICE, so listen()+close() needs only a normal local account; AF_BLUETOOTH is init_net-only (bt_sock_create), not a userns CAP_NET_ADMIN path.
- UI:NUser interaction, none
- The attacker closes their own listening L2CAP socket and, from a radio they control, sends L2CAP_CONN_REQ then disconnect; no other user must pair, accept, or confirm during the race.
- S:UScope, unchanged
- The race corrupts the host kernel l2cap_chan stored in l2cap_pi(sk)->chan of the unaccepted child; it does not escape a VM, bypass an IOMMU, or leave the kernel's own authority.
- C:HConfidentiality impact, high
- cleanup_listen loads l2cap_pi(sk)->chan then calls l2cap_chan_hold_unless_zero(); concurrent l2cap_sock_put_chan plus l2cap_conn_del's final l2cap_chan_put can kfree that object first, so kref_get_unless_zero and later l2cap_chan_lock/__set_chan_timer run on a freed kmalloc l2cap_chan that can be sprayed for disclosure.
- I:HIntegrity impact, high
- Winning that UAF lets cleanup_listen take l2cap_chan_lock, arm __set_chan_timer, and l2cap_chan_put on a reclaimed fake chan, corrupting mutex/timer/kref state and invoking chan->ops from sprayed memory for hijack.
- A:HAvailability impact, high
- If cleanup_listen observes the NULL stored by l2cap_sock_put_chan, l2cap_chan_hold_unless_zero() calls kref_get_unless_zero(&c->kref) with c==NULL and oopses; the UAF interleaving likewise panics on poisoned slab or a corrupted chan mutex.