Vulnerabilities

Vulnerability · CVE-2026-19938

The Bluetooth host's ATT transmit path releases a buffer it does not own when signing fails.

Published Oct 13, 2026 · catalog updated Oct 14, 2026 · The Bluetooth host's ATT

Check if you run it

No confirmed exploitation is on record for CVE-2026-19938. EPSS is 0.16%. Act only if a listed version of The Bluetooth host's ATT is installed.

Severity

Medium5.9

Known exploitation

Not in CISA/VulnCheck KEV

EPSS

0.16%

Remediation

Advisory link

Affected products

See sources for product scope

The Bluetooth host's ATT transmit path releases a buffer it does not own when signing fails. chan_send() in subsys/bluetooth/host/att.c documents (and every other error exit implements) the contract that on failure the caller retains ownership of the net_buf; the BT_ATT_OP_SIGNED_WRITE_CMD branch instead called net_buf_unref(buf) when bt_smp_sign() returned an error and then returned that error to the caller. The callers act on the contract: process_queue() re-queues the buffer with k_queue_prepend(), bt_att_chan_send_rsp() puts it back on chan->tx_queue, bt_att_chan_req_send() restores it into the request, and att_req_retry() unreferences it — so the already-freed buffer was re-queued, later dereferenced, and eventually freed again. An ATT Signed Write Command is produced when an application calls bt_gatt_write_without_response_cb() with sign set on an unencrypted connection. bt_smp_sign() fails whenever no local CSRK exists for the peer (-ENOENT), and whether one exists is negotiated with the peer: smp_distribute_keys() stores a local CSRK only when the peer's pairing key-distribution field requests the signing key and bonding was agreed. A peer can therefore pair without accepting the CSRK, pair with No Bonding, remain unpaired, or keep the link unencrypted, and the victim's next signed write takes the failing path. Because struct net_buf's node field is simultaneously the linkage word for the ATT TX FIFO, for the deferred-destroy list used by the att_pool destroy callback att_tx_destroy(), and for the pool free list, the mishandled buffer corrupts these lists and can be re-issued by bt_att_create_pdu() to a new PDU while the ATT TX path still holds it. The same branch also saved the net_buf_simple_state only after signing, so a buffer restored after a bt_l2cap_send_pdu() failure kept its 12-octet signature; a subsequent retry re-signed it and appended a second signature with net_buf_add(buf, 12) to a buffer that bt_att_create_pdu() sized for exactly one, writing

No affected version ranges are stored yet. Use the vendor advisory before you decide this record does not apply.