CVE-2026-10685

The Zephyr Bluetooth GATT client CCC-write response handler gatt_write_ccc_rsp() in subsys/bluetooth/host/gatt.c invoked the application&amp;#39;s params-&gt;subscribe() callback after it had already called params-&gt;notify(conn, params, NULL, 0).<br /> <br /> Per the public GATT API, a notify callback with NULL data is the documented signal that the subscription has terminated and the bt_gatt_subscribe_params struct may be freed or reused by the application; calling subscribe() on the struct afterwards is a use-after-free, including an indirect call through the freed params-&gt;subscribe function pointer.<br /> <br /> The error branch is remotely (adjacent) reachable: a Zephyr device acting as a GATT client that calls bt_gatt_subscribe() can be driven into this ordering when a connected GATT server peer answers the CCC write with an ATT Error Response (the peer-supplied error code flows through att_error_rsp -&gt; att_handle_rsp into gatt_write_ccc_rsp).<br /> <br /> For applications that free or recycle subscription parameters in their notification-termination handler, this results in memory corruption, a crash (denial of service), or potentially attacker-influenced control flow. The fix reorders the handler so the subscribe() callback runs before the terminating notify(NULL) in both the error and unsubscribe paths.