PatchSiren cyber security CVE debrief

CVE-2024-31076 Siemens CVE debrief

## Summary CVE-2024-31076 is a Linux kernel vulnerability in the x86 interrupt vector management subsystem that can cause a CPU vector resource leak during CPU hotplug operations. The issue occurs when interrupt affinity is reconfigured via procfs and the original CPU goes offline before the interrupt triggers on the new target CPU, preventing proper cleanup of the old vector allocation. ## Technical Analysis The vulnerability stems from a race condition in the interrupt migration path when `IRQD_MOVE_PCNTXT` is not set. When interrupt affinity is changed through procfs, the reconfiguration is deferred until the next interrupt trigger on the original CPU. At that point, `__irq_move_irq()` allocates a new vector on the target CPU but leaves the old vector on the original CPU marked with `apicd->move_in_progress`, deferring reclamation until the interrupt fires on the new CPU. The failure path occurs when the original CPU goes offline before the interrupt triggers on the new CPU. In this scenario, `irq_force_complete_move()` is not invoked on the outgoing CPU because `irq_needs_fixup()` returns false—the interrupt is no longer affine to that CPU. Subsequently, `__vector_schedule_cleanup()` on the new CPU resets `apicd->move_in_progress` and `apicd->prev_vector` to zero without reclaiming the vector, leaving it permanently allocated in `vector_matrix`. The kernel fix reorders operations to invoke `irq_force_complete_move()` before the `irq_needs_fixup()` check when the interrupt was previously affine to the outgoing CPU, and adds a reclamation path in `__vector_schedule_cleanup()` with appropriate warning diagnostics. ## Affected Products Per the CISA CSAF advisory ICSA-25-226-15, Siemens has identified the following affected product: - **RUGGEDCOM RST2428P (6GK6242-6PA00)** running SINEC OS The following Siemens product families were evaluated and determined **not affected**: - SCALANCE XC-300/XR-300/XC-400/XR-500WG/XR-500 family - SCALANCE XCM-/XRM-/XCH-/XRH-300 family ## Remediation Siemens provides a vendor fix: update affected RUGGEDCOM RST2428P devices to **SINEC OS V3.1 or later**. The advisory was initially published on 2025-08-12 and most repu