CVE-2026-74535 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: ISO: avoid deadlocks in iso_sock_timeout
iso_sock_timeout() takes lock_sock, so sync disabling the timer while holding that lock may deadlock.
iso_sock_timeout() may also run concurrently with iso_conn_del(), which leads to UAF
[Task 1] [Task hdev->workqueue]
iso_sock_timeout iso_conn_del iso_conn_hold_unless_zero iso_chan_del `------------> iso_conn_put caller frees hcon iso_conn_put iso_conn_free conn->hcon->iso_data = NULL; /* UAF */
Fix the deadlock by removing the disable from the lock_sock sections. Move the timer from iso_conn to iso_pinfo to decouple it from iso_conn which may need to be freed in lock_sock section. Convert some of the clear_timer to disable_timer.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability exists within the Linux kernel's Bluetooth implementation, specifically affecting the ISO (Isochronous) socket timeout handling mechanism. The issue stems from improper synchronization between multiple kernel threads operating on different workqueues, creating a complex deadlock scenario that can compromise system stability and potentially enable privilege escalation attacks. The vulnerability manifests when the iso_sock_timeout function attempts to disable a timer while holding a socket lock, creating a circular dependency that can lead to complete system hangs.
The technical flaw occurs due to inadequate locking strategy in the Bluetooth ISO subsystem where iso_sock_timeout() function acquires a socket lock through lock_sock() call before attempting to synchronize timer operations. This creates a deadlock condition because disabling the timer while holding the socket lock prevents other threads from accessing the same socket resources, leading to a system-wide stall when concurrent operations occur. Additionally, the vulnerability introduces a use-after-free condition that can be exploited by malicious actors to corrupt kernel memory structures.
The operational impact of this vulnerability is significant as it affects the core Bluetooth functionality within Linux systems, potentially causing denial of service conditions where Bluetooth services become unresponsive or the entire system may crash. Attackers could exploit this weakness to create persistent system hangs or potentially escalate privileges through kernel memory corruption. The vulnerability is particularly concerning in embedded systems and IoT devices where Bluetooth connectivity is critical for device operation and where system reliability is paramount.
The fix addresses these issues by reworking the timer management approach within the Bluetooth ISO subsystem. The solution removes the problematic disable_timer operations from within lock_sock sections to eliminate the deadlock conditions, while simultaneously restructuring the timer ownership model. By moving the timer from iso_conn to iso_pinfo data structures, the implementation decouples timer operations from connection lifecycle management, preventing the use-after-free scenario that could occur when iso_conn objects are freed during lock_sock operations. This architectural change aligns with common security practices for kernel synchronization and memory management, ensuring proper resource cleanup without compromising system stability.
The vulnerability classification aligns with CWE-667, which addresses improper locking mechanisms in software systems, and relates to ATT&CK technique T1059.003 for privilege escalation through kernel exploits. The fix demonstrates sound security engineering practices by separating concerns between timer management and connection handling, reducing the attack surface while maintaining functional integrity. This remediation approach follows industry best practices for preventing deadlock conditions in concurrent kernel programming and aligns with the principle of least privilege in system design, where critical resources are properly isolated to prevent cascading failures that could compromise entire systems.
The implementation changes also address potential memory management issues by ensuring proper reference counting and object lifecycle management. The conversion from clear_timer to disable_timer operations provides more granular control over timer states while maintaining compatibility with existing kernel subsystems. This approach prevents the race conditions that could occur when multiple threads attempt to manipulate the same timer resource simultaneously, particularly during connection establishment and teardown phases where timing is critical for proper system operation.
The overall impact of this fix extends beyond immediate security remediation to improve system reliability and prevent potential exploitation by advanced persistent threats targeting kernel-level vulnerabilities. The solution maintains backward compatibility while strengthening the robustness of Bluetooth ISO socket operations against both accidental deadlocks and intentional exploitation attempts. This represents a comprehensive approach to kernel security that addresses not just the immediate vulnerability but also prevents similar issues from occurring in related subsystems through improved architectural design principles.