CVE-2023-54038 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: hci_conn: return ERR_PTR instead of NULL when there is no link
hci_connect_sco currently returns NULL when there is no link (i.e. when hci_conn_link() returns NULL).
sco_connect() expects an ERR_PTR in case of any error (see line 266 in sco.c). Thus, hcon set as NULL passes through to sco_conn_add(), which tries to get hcon->hdev, resulting in dereferencing a NULL pointer as reported by syzkaller.
The same issue exists for iso_connect_cis() calling hci_connect_cis().
Thus, make hci_connect_sco() and hci_connect_cis() return ERR_PTR instead of NULL.
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Analysis
by VulDB Data Team • 12/26/2025
The vulnerability described in CVE-2023-54038 represents a critical null pointer dereference flaw within the Linux kernel's Bluetooth subsystem that stems from improper error handling in connection establishment functions. This issue affects the HCI (Host Controller Interface) layer where Bluetooth connections are managed, specifically impacting the SCO (Synchronous Connection-Oriented) and ISO (Isochronous) connection types. The flaw occurs when the hci_conn_link() function fails to establish a connection link and returns NULL, but the calling functions hci_connect_sco() and hci_connect_cis() do not properly handle this error condition by returning ERR_PTR instead of NULL. This inconsistency creates a scenario where downstream functions expect error pointers but receive NULL values, leading to kernel memory corruption and potential system crashes.
The technical root cause of this vulnerability lies in the mismatch between expected and actual return values within the Bluetooth connection establishment pipeline. When hci_connect_sco() encounters a failed link connection, it returns NULL instead of an error pointer as required by the calling convention established in the sco_connect() function. This violation of expected interface behavior causes the system to proceed with a NULL pointer dereference operation when sco_conn_add() attempts to access hcon->hdev without proper validation. The issue is further compounded by the identical flaw present in iso_connect_cis() which calls hci_connect_cis(), demonstrating a systemic problem in how error conditions are handled across multiple connection types within the same kernel subsystem. According to CWE-476, this represents a NULL Pointer Dereference vulnerability where a null pointer is dereferenced, potentially leading to arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple system crashes to potentially enable privilege escalation and denial of service attacks within Bluetooth-enabled systems. Attackers could exploit this flaw by triggering Bluetooth connection attempts that fail in specific ways, causing the kernel to crash or behave unpredictably. The vulnerability is particularly concerning in embedded systems, mobile devices, and IoT appliances that rely heavily on Bluetooth connectivity, as these environments may not have robust error handling or recovery mechanisms. The issue was identified through systematic testing with syzkaller, a powerful fuzzer designed to discover kernel-level vulnerabilities, indicating that the flaw could be reliably reproduced and potentially exploited in real-world scenarios. From an ATT&CK framework perspective, this vulnerability could be leveraged in initial access or privilege escalation phases, particularly when targeting systems where Bluetooth functionality is enabled and accessible to untrusted users.
The mitigation strategy for this vulnerability requires immediate kernel updates that implement the fix by modifying hci_connect_sco() and hci_connect_cis() to return ERR_PTR instead of NULL when connection establishment fails. This change ensures proper error propagation through the Bluetooth connection stack and prevents the NULL pointer dereference that leads to kernel crashes. System administrators should prioritize patching affected Linux kernel versions, particularly those running on devices with active Bluetooth functionality. Additionally, monitoring for Bluetooth-related system crashes or unexpected reboots may help identify exploitation attempts. Organizations should also consider implementing Bluetooth access controls and limiting unnecessary Bluetooth functionality on critical systems. The fix aligns with standard kernel security practices for error handling and demonstrates the importance of maintaining consistent interface contracts within kernel subsystems, as outlined in security guidelines for kernel development and maintenance.