CVE-2026-98268 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
perf: Fix null pointer access in is_include_guest_event()
A typical module unload occurring event when there is an active perf connection leads to freeing of the pmu pointer. The call log is something like: .. __pmu_detach_event pmu_detach_event pmu_detach_events perf_pmu_unregister ..
__pmu_detach_event() sets event->pmu to null. When the perf connection finally is closed, the following stack trace is observed:
Oops: general protection fault, kernel NULL pointer dereference ... RIP: 0010:_free_event+0x3e/0x370 ... Call Trace: ... perf_event_release_kernel+0x260/0x2d0 perf_release+0x12/0x20
A call to mediated_pmu_unaccount_event() inside _free_event() is the root cause of this crash. Adding a check inside is_include_guest_event() ensures we don't accidentally access a null pmu ptr. In addition to this, we will now call mediated_pmu_unaccount_event() before clearing the pmu ptr so that nr_include_guest_events counts are maintained correctly.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel's performance monitoring subsystem contains a critical vulnerability involving improper handling of pointer lifecycles during module unloading and event release sequences. This flaw manifests as a null pointer dereference within the perf subsystem, specifically triggered when an active performance measurement connection exists while a related hardware unit is being unloaded or deregistered. The root cause lies in the sequence of operations performed by the kernel's power management unit detachment logic. When a module unload occurs, the function __pmu_detach_event() is invoked as part of the pmu_detach_events and perf_pmu_unregister flow. This function explicitly sets the event->pmu field to null before the associated performance events are fully cleaned up or released by user-space applications holding open file descriptors for those events.
The vulnerability is exploited when a process subsequently closes its connection to the perf subsystem, triggering the release of the underlying perf_event structures via perf_release and perf_event_release_kernel. During this cleanup phase, the kernel attempts to free the event resources through _free_event. Inside this function, there is an unconditional call to mediated_pmu_unaccount_event(), which in turn invokes is_include_guest_event(). Because the pmu pointer was already nullified by the earlier detachment process, is_include_guest_event() attempts to dereference a null address, resulting in a general protection fault and kernel NULL pointer dereference. This crash can lead to system instability or denial of service for any user relying on performance monitoring capabilities within that kernel instance.
From a technical classification perspective, this vulnerability aligns with CWE-476, which describes a NULL Pointer Dereference error. The flaw represents an improper check before resource access, where the code fails to verify whether the pmu pointer is valid before attempting to use it for guest event inclusion checks. In terms of attack vectors and tactical mapping under MITRE ATT&CK, this issue relates to T1499 Endpoint Denial of Service, as a local attacker with sufficient privileges to open perf events can trigger a kernel panic by carefully timing the module unload relative to connection closure. It also touches upon privilege escalation risks if such crashes are leveraged in conjunction with other vulnerabilities to disrupt security controls or cause system reboots that bypass certain stateful protections.
The operational impact of this vulnerability is primarily centered on system reliability and availability rather than direct data exfiltration or code execution, although the resulting kernel panic can be used as a denial-of-service vector against critical infrastructure services running performance monitoring tools. To mitigate this risk, developers have implemented two key fixes within the perf subsystem logic. First, a null pointer check was added to is_include_guest_event() to ensure that access to pmu-related data structures only occurs when the pointer is valid and non-null. Second, the order of operations in _free_event() was adjusted so that mediated_pmu_unaccount_event() is called before clearing the pmu pointer. This ensures that reference counts for guest events are maintained correctly throughout the lifecycle of the event object, preventing premature invalidation of pointers while they are still being accessed by cleanup routines.
Administrators and developers should ensure their Linux kernels are updated to versions containing this patch to prevent potential crashes during routine maintenance or dynamic module loading scenarios involving performance monitoring tools. The fix addresses both the immediate crash vector and the underlying state management issue regarding event accounting, thereby restoring robustness to the perf subsystem under concurrent unload and release conditions.