CVE-2026-99187 in Linux
Summary
by MITRE • 10/28/2026
In the Linux kernel, the following vulnerability has been resolved:
perf: Fix perf_pmu_migrate_context() leaving events behind
__perf_pmu_remove() walks the group leaders of a CPU and PMU with perf_event_groups_for_cpu_pmu(), removing each one as it goes. perf_remove_from_context() takes the leader out of the groups rbtree, after which rb_next() on that node returns NULL, prematurely ending the walk. Other groups stay behind in the source context.
On CPU hotplug, they are then torn down with the dying CPU. They keep running until teardown, while the PMU's interrupt and migrated events are on a new CPU, which drivers rely on never happening.
Walk ctx->event_list instead and pick out the PMU's events by their pmu_ctx.
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Analysis
by VulDB Data Team • 10/28/2026
The Linux kernel perf subsystem contains a critical logic flaw within the performance monitoring unit context migration mechanism that can lead to resource leaks and inconsistent hardware state during CPU hotplug operations. The vulnerability resides in the implementation of __perf_pmu_remove, which is responsible for cleaning up performance events associated with a specific Performance Monitoring Unit on a given Central Processing Unit when that CPU is being removed or migrated. This function utilizes perf_event_groups_for_cpu_pmu to iterate through group leaders belonging to the target CPU and PMU combination. The core technical error occurs during the removal process where perf_remove_from_context is invoked to detach an event from its context's red-black tree structure. Because this operation modifies the rbtree in place, subsequent calls to rb_next on the current node return NULL instead of pointing to the next valid group leader. This premature termination causes the iteration loop to exit before all relevant events have been processed and removed from their original contexts.
As a direct consequence of this traversal failure, performance event groups remain orphaned within the source context rather than being properly migrated or destroyed. These lingering events continue to operate in an undefined state while the associated PMU interrupts and other migrated events are correctly assigned to a new CPU core during the hotplug transition. This discrepancy creates a dangerous operational scenario where legacy hardware interactions persist on the dying CPU despite the software expecting them to have moved. Many underlying driver implementations rely heavily on the assumption that once a migration or removal sequence is initiated, no residual events will continue executing on the old processor. The persistence of these stale event contexts violates this implicit contract between the kernel perf subsystem and its drivers, potentially leading to hardware conflicts, incorrect performance data collection, or system instability if the dying CPU attempts to service interrupts for events that are logically considered migrated elsewhere.
The operational impact extends beyond mere resource leakage into potential security and stability risks. If an attacker can influence CPU hotplug scenarios or trigger specific perf event group configurations, they might exploit this state inconsistency to maintain unauthorized access to performance monitoring capabilities even after a context switch intended to isolate them. Furthermore, the continued execution of these events on a shutting down CPU core may cause race conditions with hardware registers that are being reconfigured for the new CPU affinity, leading to unpredictable kernel behavior or crashes. This flaw effectively undermines the integrity of the perf subsystem's resource management guarantees during dynamic topology changes, which are common in virtualized environments and systems utilizing advanced power management features like hot-pluggable cores.
To mitigate this vulnerability, the Linux kernel developers have implemented a fix that alters the iteration strategy within __perf_pmu_remove. Instead of relying on rb_next to traverse group leaders after removal operations disrupt the tree structure, the corrected code walks ctx->event_list directly and filters events based on their pmu_ctx attribute. This approach ensures that all relevant performance monitoring unit contexts are identified and processed regardless of the structural changes caused by removing individual nodes from the red-black tree. By decoupling the iteration logic from the mutable rbtree state during removal, the fix guarantees complete cleanup of orphaned groups before the CPU context is torn down.
From a classification perspective, this vulnerability aligns with CWE-401, which describes a missing release of memory after successful allocation or improper handling of resources leading to resource leaks. The failure to properly remove events from their contexts constitutes an incomplete cleanup that leaves dangling references and active hardware interactions in an invalid state. In terms of the MITRE ATT&CK framework, this flaw relates to techniques involving persistence through system processes or components where residual artifacts allow continued operation despite intended removal actions. While primarily a stability issue, the potential for maintaining unauthorized monitoring capabilities places it within the scope of defense evasion tactics if exploited maliciously in conjunction with other vulnerabilities. System administrators and developers should ensure that kernel updates incorporating this perf subsystem fix are applied promptly to restore correct resource lifecycle management during CPU hotplug events and prevent the accumulation of stale performance event contexts.