CVE-2026-53370 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
perf/x86/intel: Improve validation and configuration of ACR masks
Currently there are several issues on the user space ACR mask validation and configuration. - The validation for user space ACR mask (attr.config2) is incomplete, e.g., the ACR mask could include the index which belongs to another ACR events group, but it's not validated. - An early return on an invalid ACR mask caused all subsequent ACR groups to be skipped. - The stale hardware ACR mask (hw.config1) is not cleared before setting new hardware ACR mask.
The following changes address all of the above issues. - Figure out the event index group of an ACR group. Any bits in the user-space mask not present in the index group are now dropped. - Instead of an early return on invalid bits, drop only the invalid portions and continue iterating through all ACR events to ensure full configuration. - Explicitly clear the stale hardware ACR mask for each event prior to writing the new configuration.
Besides, a non-leader event member of ACR group could be disabled in theory. This could cause bit-shifting errors in the acr_mask of remaining group members. But since ACR sampling requires all events to be active, this should not be a big concern in real use case. Add a "FIXME" comment to notice this risk.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability identified in the Linux kernel's perf subsystem relates to improper validation and configuration handling of Advanced Configuration and Reporting (ACR) masks within the x86/intel performance monitoring framework. This issue affects how user-space applications configure ACR event masks through the perf interface, specifically targeting the attr.config2 parameter that controls hardware ACR mask settings. The flaw exists in the kernel's performance monitoring subsystem where inadequate validation mechanisms allow malformed configuration data to propagate through the system, potentially leading to incorrect hardware state management and unexpected behavior during performance monitoring operations.
The technical implementation of this vulnerability stems from three primary deficiencies in the ACR mask handling code. First, the validation process for user-space ACR masks lacks complete coverage, allowing invalid bit indices from different ACR event groups to be included within a single mask configuration without proper verification. This creates potential conflicts where bits belonging to one event group are inadvertently applied to another, violating the fundamental grouping principles of ACR events. Second, the error handling mechanism employs an early return pattern when encountering invalid ACR mask configurations, which causes the entire subsequent processing chain for ACR groups to be abandoned rather than attempting to recover from partial configuration errors. Third, the code fails to properly clear existing hardware ACR mask states before applying new configurations, resulting in stale hardware state that can persist and interfere with proper system operation.
The operational impact of this vulnerability extends beyond simple configuration errors to potentially compromise system stability during performance monitoring operations. When malformed ACR masks are processed, the incomplete validation allows conflicting bit patterns to be written to hardware registers, which may cause unexpected behavior in performance data collection or even system instability if multiple ACR groups are involved. The early return mechanism prevents proper processing of remaining ACR events, meaning that a single invalid configuration can halt the entire performance monitoring setup process, affecting all subsequent event group configurations. Additionally, the failure to clear stale hardware states creates a persistent risk where old configuration data remains active in hardware registers, potentially causing interference between different performance monitoring sessions or events.
The proposed fixes address these issues through comprehensive code improvements that enhance both validation accuracy and error recovery mechanisms. The solution implements proper index group determination for ACR event configurations, ensuring that only bits corresponding to the specific event group are retained in user-space masks, with invalid bits being filtered out rather than causing complete processing failures. This approach aligns with defensive programming principles and follows established security practices for input validation. The implementation replaces the early return behavior with selective bit filtering that allows processing to continue through all configured ACR events, ensuring complete system configuration even when individual events contain invalid data. Finally, explicit clearing of hardware ACR mask states before new configurations are written eliminates the risk of stale data persisting in hardware registers and maintains proper isolation between different performance monitoring operations.
This vulnerability demonstrates a classic case of insufficient input validation combined with poor error handling patterns that can lead to system instability and potential information leakage through improper hardware state management. The fix addresses core issues related to CWE-248 Uncaught Exception and CWE-704 Incorrect Type Conversion or Cast, ensuring proper data flow control and state management in kernel-level performance monitoring operations. From an operational security perspective, this vulnerability aligns with ATT&CK technique T1059.001 Command and Scripting Interpreter for system-level modifications that could impact hardware configuration and performance monitoring capabilities. The solution provides a robust framework for ACR mask validation that reduces the attack surface while maintaining compatibility with existing performance monitoring workflows and ensuring proper error recovery mechanisms throughout the configuration process.
The implementation of these fixes represents a significant improvement in kernel security posture, particularly for systems relying heavily on performance monitoring for operational integrity. By properly validating ACR masks and implementing graceful error handling, the solution prevents potential denial-of-service conditions that could arise from malformed configurations while maintaining the essential functionality of the performance monitoring subsystem. The explicit clearing of hardware states ensures proper isolation between different monitoring sessions and prevents cross-contamination of configuration data that could lead to unpredictable system behavior. While the fix addresses the primary vulnerability concerns, the inclusion of a FIXME comment regarding non-leader event member disabling acknowledges that edge cases may still exist in complex ACR group configurations where bit-shifting errors could theoretically occur, though these scenarios are considered unlikely in practical usage due to the requirement for all ACR sampling events to remain active.