CVE-2026-11368: Zephyr Use After Free (CVSS 6.5)

Description

The Bluetooth host ATT layer (subsys/bluetooth/host/att.c) associates each in-flight ATT TX buffer with its owning channel via the static tx_meta_data_storage[] array (data->att_chan = chan). When a buffer's last reference is dropped, its net-buf destroy callback defers the completion handling to the system workqueue (att_tx_destroy -> att_tx_destroy_work_handler -> att_on_sent_cb -> bt_att_sent), where bt_att_sent dereferences the channel and its ATT context (sys_slist_get(&att->reqs)). When a peer disconnects while an ATT PDU (a server notification/indication or any response) is still in flight in the controller TX path, L2CAP tears the channel down in l2cap_chan_del(): it runs the disconnected callback and then the released callback (bt_att_released), which frees the channel slab slot. Because the in-flight buffer is held by the connection TX path rather than the channel's own queue, its deferred destroy work can run after the channel has been freed. The att_on_sent_cb guard intended to drop the stale callback itself dereferences meta->att_chan, which is now a dangling pointer into a freed (and possibly reused) slab slot. A remote peer with an ATT connection can drive this by disconnecting during routine ATT traffic; no pairing or user interaction is required to reach the ATT bearer. The result is a use-after-free read/write of freed channel memory, reliably crashing the Bluetooth host (denial of service) and, because the channel slab slot may be reused, potentially corrupting live memory. The fix makes bt_att_released() NULL the att_chan field of every tx_meta_data_storage[] entry still referencing the channel before freeing it, so the deferred guard observes a NULL pointer and drops the callback. Teardown and the destroy work both run on the cooperative system workqueue, so the array update is serialized and needs no lock.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.28%

20.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-416

Affected Software

Vendor	Product	Versions
Zephyrproject	Zephyr	>= 4.4.0, < 4.5.0

References

https://github.com/zephyrproject-rtos/zephyr/commit/dfdea9bad8d9b5b31c125e97fcffb549f2217caaPatch
https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-85vg-gwc4-77g7Exploit, Patch, Vendor Advisory

Timeline

Published: Aug 4, 2026
Last Modified: Sep 1, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-11368?

The Bluetooth host ATT layer (subsys/bluetooth/host/att.c) associates each in-flight ATT TX buffer with its owning channel via the static tx_meta_data_storage[] array (data->att_chan = chan). When a buffer's last reference is dropped, its net-buf destroy callback defers the completion handling to the system workqueue (att_tx_destroy -> att_tx_destroy_work_handler -> att_on_sent_cb -> bt_att_sent), where bt_att_sent dereferences the channel and its ATT context (sys_slist_get(&att->reqs)). When a peer disconnects while an ATT PDU (a server notification/indication or any response) is still in flight in the controller TX path, L2CAP tears the channel down in l2cap_chan_del(): it runs the disconnected callback and then the released callback (bt_att_released), which frees the channel slab slot. Because the in-flight buffer is held by the connection TX path rather than the channel's own queue, its deferred destroy work can run after the channel has been freed. The att_on_sent_cb guard intended to drop the stale callback itself dereferences meta->att_chan, which is now a dangling pointer into a freed (and possibly reused) slab slot. A remote peer with an ATT connection can drive this by disconnecting during routine ATT traffic; no pairing or user interaction is required to reach the ATT bearer. The result is a use-after-free read/write of freed channel memory, reliably crashing the Bluetooth host (denial of service) and, because the channel slab slot may be reused, potentially corrupting live memory. The fix makes bt_att_released() NULL the att_chan field of every tx_meta_data_storage[] entry still referencing the channel before freeing it, so the deferred guard observes a NULL pointer and drops the callback. Teardown and the destroy work both run on the cooperative system workqueue, so the array update is serialized and needs no lock.

How severe is CVE-2026-11368?

CVE-2026-11368 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.28% probability of exploitation in the next 30 days.

How do I fix CVE-2026-11368?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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