CVE-2026-64477 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
x86,fs/resctrl: Prevent out-of-bounds access while offlining CPU when SNC enabled
The architecture updates the cpu_mask in a domain's header to track which online CPUs are associated with the domain. When this mask becomes empty the architecture initiates offline of the domain that includes calling on resctrl fs to offline the domain. If it is a monitoring domain in which LLC occupancy is tracked resctrl fs forces the limbo handler to clear all busy RMID state associated with the domain.
The limbo handler always reads the current event value associated with a busy RMID irrespective of it being checked as part of regular "is it still busy" check or whether it will be forced released anyway. When reading an RMID on a system with SNC enabled the "logical RMID" is converted to the "physical RMID" and this conversion requires the NUMA node ID of the resctrl monitoring domain that is in turn determined by querying the NUMA node ID of any CPU belonging to the monitoring domain.
When the monitoring domain is going offline its cpu_mask is empty causing the NUMA node ID query via cpu_to_node() to be done with "nr_cpu_ids" as argument resulting in an out-of-bounds access.
Refactor the limbo handler to skip reading the RMID when the RMID will just be forced to no longer be dirty in the domain anyway. Add a safety check to the architecture's RMID reader to protect against this scenario.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability exists within the Linux kernel's x86 architecture implementation related to Resource Control (resctrl) filesystem functionality and Scalable Node Cache (SNC) support. The issue manifests when a monitoring domain is being offline while SNC is enabled, creating a scenario where out-of-bounds memory access occurs during the cleanup process. The kernel's resource control subsystem manages cache allocation through Last Level Cache (LLC) occupancy tracking, which requires careful handling of RMID (Resource Monitoring ID) states during CPU online/offline operations.
The technical flaw stems from improper bounds checking in the limbo handler component that processes RMID state cleanup when domains go offline. During normal operation, the architecture maintains a cpu_mask in each domain's header to track online CPUs associated with that domain. When all CPUs are removed from this mask, the system initiates domain offline processing through resctrl filesystem calls. The problematic behavior occurs when monitoring domains that track LLC occupancy attempt to clear busy RMID states, as the limbo handler reads current event values from RMIDs without proper validation.
The vulnerability is particularly dangerous because it leverages the SNC-specific RMID conversion logic where logical RMIDs are translated to physical RMIDs based on NUMA node identification. When processing an offline domain with an empty cpu_mask, the system calls cpu_to_node() with nr_cpu_ids as parameter instead of a valid CPU ID, resulting in memory access beyond the allocated CPU array bounds. This constitutes a classic out-of-bounds read vulnerability that can lead to information disclosure, system instability, or potential privilege escalation depending on exploitation context.
The operational impact extends beyond simple memory corruption since this vulnerability affects systems with SNC enabled where cache monitoring is actively used for resource allocation and performance tracking. Attackers could potentially exploit this through kernel memory corruption to gain elevated privileges or cause denial of service conditions. The issue represents a violation of proper bounds checking principles and demonstrates inadequate validation of CPU mask states during domain offline operations, aligning with CWE-129 Input Validation and CWE-787 Out-of-bounds Write patterns.
Mitigation strategies include refactoring the limbo handler to skip RMID reading when the RMID state will be forcibly cleared anyway, preventing unnecessary access to potentially invalid memory regions. Additionally, adding safety checks in the architecture's RMID reader component protects against scenarios where cpu_to_node() might receive invalid arguments due to empty CPU masks during domain offline processing. These changes align with ATT&CK technique T1068 Exploitation for Privilege Escalation and T1547.001 Registry Run Keys/Startup Folder persistence mechanisms, as they address fundamental kernel memory safety issues that could enable privilege escalation attacks. The fix ensures proper state validation before memory access operations and prevents the propagation of invalid CPU identifiers through the NUMA node identification chain, thereby protecting against potential exploitation vectors targeting kernel memory corruption vulnerabilities.