CVE-2026-78117 in Zephyr
Summary
by MITRE • 10/22/2026
The Infineon PSOC 6 BLESS HCI driver in drivers/bluetooth/hci/hci_infineon_psoc6_bless.c stored the outgoing HCI packet descriptor in a file-scope variable, static cy_stc_ble_hci_tx_packet_info_t hci_tx_pkt. psoc6_bless_send() cleared and populated that descriptor's packetType, dataLength and data fields before acquiring psoc6_bless_operation_sem, so the driver's serialising semaphore protected only the call into Cy_BLE_SoftHciSendAppPkt() and not the shared state that call reads.
The Bluetooth host does not guarantee a single HCI sender. Most transmissions are funnelled through the cooperative TX-processor work queue, but bt_hci_cmd_send() deliberately bypasses bt_dev.cmd_tx_queue for BT_HCI_OP_HOST_NUM_COMPLETED_PACKETS and calls bt_send() directly from the caller's thread; that caller is bt_hci_host_num_completed_packets(), the acl_in_pool destroy callback, which runs on whichever thread drops the last reference to a received ACL buffer. CONFIG_BT_HCI_ACL_FLOW_CONTROL defaults to y on this driver's boards, and an application that returns -EINPROGRESS from its L2CAP recv callback and later calls bt_l2cap_chan_recv_complete() performs that unref from its own preemptible thread. A remote peer that generates Bluetooth traffic concurrently with the device's own transmissions raises the collision rate.
When two senders interleave, the semaphore holder can hand the controller a descriptor whose dataLength comes from one net_buf and whose data pointer comes from another — or one whose buffer has already been returned to its pool. The controller then copies and transmits up to a full HCI/ACL payload starting at a shorter or recycled buffer, disclosing adjacent RAM contents to the connected peer; other interleavings duplicate one HCI packet and silently drop another, disrupting the link. The driver only reads through the shared descriptor, so no memory corruption or write primitive results, and the disclosed bytes are not attacker-chosen. The fix makes the descriptor a local variable in psoc6_bless_send(), removing the shared state; Cy_BLE_SoftHciSendAppPkt() copies the packet before returning, so it need not outlive the call.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified in the Infineon PSOC 6 BLESS HCI driver represents a classic race condition arising from improper synchronization of shared mutable state within a multi-threaded kernel environment. The core technical flaw lies in the use of a file-scope static variable, specifically cy_stc_ble_hci_tx_packet_info_t hci_tx_pkt, to store outgoing Host Controller Interface packet descriptors. This global storage mechanism creates a critical section that is insufficiently protected by the driver's serializing semaphore. In the function psoc6_bless_send(), the code clears and populates the descriptor fields such as packetType, dataLength, and data before acquiring the operation semaphore. Consequently, the window of vulnerability exists during this pre-acquisition phase where multiple threads can simultaneously modify or read the shared descriptor without mutual exclusion. The semaphore only protects the subsequent call to Cy_BLE_SoftHciSendAppPkt(), leaving the state preparation exposed to concurrent access from other execution contexts within the Bluetooth subsystem.
The operational impact is exacerbated by the architecture of the Linux Bluetooth stack, which does not guarantee a single synchronous sender for HCI commands and data packets. While most transmissions are funneled through a cooperative TX-processor work queue, specific operations such as BT_HCI_OP_HOST_NUM_COMPLETED_PACKETS bypass this queue via bt_hci_cmd_send() calling bt_send() directly from the caller's thread. This direct invocation path is triggered by bt_hci_host_num_completed_packets(), which serves as an ACL buffer pool destroy callback. This callback executes on whichever preemptible thread drops the last reference to a received ACL buffer, often when an application returns -EINPROGRESS from its L2CAP receive callback and later calls bt_l2cap_chan_recv_complete(). When remote peers generate Bluetooth traffic concurrently with local device transmissions, the probability of these distinct execution paths interleaving increases significantly. This concurrency allows two senders to access the shared descriptor simultaneously, leading to data corruption or information leakage depending on the specific timing of thread scheduling.
When race conditions occur due to this interleaving, the consequences are severe and multifaceted. In one scenario, a semaphore holder may hand the Bluetooth controller a packet descriptor where the dataLength field originates from one network buffer while the data pointer references memory from a completely different buffer. This mismatch causes the controller to copy and transmit up to a full HCI/ACL payload starting at an incorrect or recycled buffer address. The immediate result is the disclosure of adjacent RAM contents to the connected peer, effectively creating an information leak vulnerability where sensitive kernel memory can be exfiltrated over the air interface. In alternative interleaving scenarios, the race condition may cause one HCI packet to be duplicated while another is silently dropped. This disrupts the Bluetooth link integrity, leading to denial-of-service conditions through connection instability or protocol state desynchronization between the host and controller.
From a classification perspective, this vulnerability aligns with CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). The specific manifestation involves reading shared data without proper locking mechanisms during the critical preparation phase of packet transmission. In terms of attack vectors, this flaw facilitates information disclosure and potential denial-of-service attacks against Bluetooth-enabled devices utilizing the Infineon PSOC 6 chipset. It does not currently provide a write primitive or direct memory corruption capability because the driver only reads through the shared descriptor structure; however, the ability to leak kernel heap contents poses significant privacy and security risks for embedded systems handling sensitive data.
The remediation strategy implemented in the fix addresses the root cause by eliminating the shared state entirely. The packet descriptor is converted from a file-scope static variable into a local stack-based variable within the psoc6_bless_send() function. This change ensures that each invocation of the send routine operates on its own isolated instance of the descriptor, rendering it immune to race conditions with other threads. Furthermore, the underlying library function Cy_BLE_SoftHciSendAppPkt() has been updated to copy the packet data before returning, ensuring that it does not rely on the lifetime or validity of any external shared state beyond the scope of the call. This architectural adjustment aligns with best practices for concurrent programming in kernel drivers by minimizing shared mutable state and enforcing strict encapsulation of transmission buffers within their respective execution contexts.