CVE-2026-99013 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: ISO: Reject concurrent BIS listener setup
iso_sock_listen() drops the socket lock before calling iso_listen_bis() to preserve the hdev->lock ordering. Two concurrent listen() calls on the same broadcast socket can therefore both observe BT_BOUND. Caller A can attach connA and release the locks, then caller B can acquire them and attach connB before A publishes BT_LISTEN.
__iso_chan_add() checks whether connB already has a socket, but not whether the socket already has a connection. The second attachment overwrites iso_pi(sk)->conn, leaking the connA reference and leaving connA->sk intact. Socket teardown follows connB, so later events on connA can cause a stale socket access.
Recheck BT_BOUND and require iso_pi(sk)->conn to be NULL after taking both the HCI device and socket locks in iso_listen_bis(). The connection check also covers the interval between attachment and publication of BT_LISTEN. Reject a competing setup with -EBADFD through the existing unlock path before allocating another connection.
A recorded KASAN report from an instrumented kernel shows:
BUG: KASAN: slab-use-after-free in iso_sock_hold+0x119/0x1f0 Call Trace: iso_sock_hold+0x119/0x1f0 iso_conn_del+0xe4/0x270 hci_disconn_complete_evt+0x351/0x8c0 hci_event_packet+0x71b/0xb20 hci_rx_work+0x293/0x730
Allocated by task 93: sk_prot_alloc+0x113/0x220 sk_alloc+0x2b/0x6d0 bt_sock_alloc+0x29/0x370 iso_sock_alloc.constprop.0+0x19/0x300 iso_sock_create+0x94/0x100
Freed by task 93: kfree+0x121/0x3c0 __sk_destruct+0x42b/0x540 iso_sock_release+0x29d/0x340 __sock_release+0xa1/0x260 sock_close+0x10/0x20
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Analysis
by VulDB Data Team • 10/23/2026
The Linux kernel Bluetooth subsystem contains a race condition vulnerability within the Isochronous Channels (ISO) implementation, specifically affecting Broadcast ISO Service (BIS) listener setup. This flaw arises from improper synchronization during socket state transitions when handling concurrent listen operations on the same broadcast socket. The core issue lies in iso_sock_listen(), which intentionally drops the socket lock before invoking iso_listen_bis() to maintain correct locking hierarchy with hdev->lock. While this design prevents deadlocks, it creates a critical window where two separate threads can simultaneously observe the BT_BOUND state and proceed with connection attachment without mutual exclusion. This timing gap allows for a race condition that compromises memory safety and leads to use-after-free scenarios.
The technical mechanism of exploitation involves multiple steps triggered by concurrent calls to listen() on an ISO socket. When the first caller, referred to as Caller A, attaches its connection object connA and releases the locks, it has not yet published the BT_LISTEN state. Before this publication occurs, a second caller, Caller B, acquires the necessary locks and proceeds to attach its own connection object connB. The function __iso_chan_add() performs a check to ensure that connB does not already have an associated socket, but critically fails to verify whether the target socket already has an active connection attached. Consequently, the attachment of connB overwrites the iso_pi(sk)->conn pointer in the socket structure. This action leaks the reference count for connA while leaving its sk field intact and pointing to a now-invalidated or detached context.
The operational impact of this vulnerability is severe, resulting in a slab-use-after-free condition that can lead to kernel crashes, data corruption, or potential privilege escalation depending on memory layout exploitation opportunities. Because socket teardown logic follows the lifecycle of connB, any subsequent HCI events related to connA will attempt to access the stale socket pointer left behind by the overwritten connection reference. This results in invalid memory accesses as demonstrated by Kernel Address Sanitizer (KASAN) reports showing faults within iso_sock_hold during disconnection completion events. The vulnerability effectively allows an attacker with local access to trigger a denial of service or potentially execute arbitrary code through careful manipulation of Bluetooth ISO socket states and timing attacks against the lock release window.
This flaw is categorized under CWE-362, Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition), as it stems from inadequate locking during state transitions in multi-threaded environments. It also aligns with ATT&CK technique T1059, Command and Scripting Interpreter, if leveraged for further exploitation within the kernel space to execute arbitrary commands via memory corruption primitives. The vulnerability highlights the complexity of maintaining lock ordering while preventing race conditions in network stack implementations where state changes must be atomic relative to other subsystem events.
Mitigation strategies primarily involve applying the upstream Linux kernel patch that addresses this specific race condition by rechecking the BT_BOUND status and ensuring iso_pi(sk)->conn is NULL after acquiring both HCI device and socket locks within iso_listen_bis(). This additional validation closes the window between connection attachment and state publication, effectively rejecting competing setups with an -EBADFD error code before any new connections are allocated. System administrators should ensure that their systems are updated to kernel versions containing this fix. For environments where immediate patching is not feasible, restricting access to Bluetooth ISO socket creation and limiting user privileges for applications requiring such functionality can reduce the attack surface. Continuous monitoring of system logs for KASAN reports or unusual Bluetooth disconnection patterns may also aid in detecting attempted exploitation activities.