CVE-2026-23271: Linux Kernel Race Condition Vulnerability

CVE-2026-23271 Overview

A race condition vulnerability has been identified in the Linux kernel's performance monitoring subsystem (perf). The vulnerability exists in the __perf_event_overflow() function, which fails to run with interrupts (IRQs) disabled for all possible callchains. Specifically, software events can execute this function with only preemption disabled, creating a race condition against perf_event_exit_event() and related functions that free resources expected to be present during the overflow path, including BPF programs.

Critical Impact

This race condition can lead to use-after-free scenarios where the overflow path accesses freed memory, potentially causing kernel crashes, data corruption, or system instability.

Affected Products

• Linux Kernel (multiple versions)
• Systems utilizing the perf subsystem with software events
• Environments running BPF programs attached to perf events

Discovery Timeline

• 2026-03-20 - CVE CVE-2026-23271 published to NVD
• 2026-03-25 - Last updated in NVD database

Technical Details for CVE-2026-23271

Vulnerability Analysis

The vulnerability stems from improper synchronization in the Linux kernel's performance event handling subsystem. The __perf_event_overflow() function is designed to handle performance counter overflow events, but the current implementation does not guarantee that IRQs are disabled during its execution for all code paths.

When software-based performance events trigger, the function may execute with only preemption disabled rather than having IRQs fully disabled. This creates a timing window where concurrent operations can interfere with the overflow handling process.

The perf_remove_from_context() function, called by perf_event_exit_event(), can free critical resources such as BPF programs while __perf_event_overflow() is still attempting to access them. This race condition can result in use-after-free conditions when the overflow handler attempts to execute or reference a BPF program that has already been deallocated.

Root Cause

The root cause is insufficient interrupt protection in the __perf_event_overflow() function. While hardware performance events naturally run in interrupt context with IRQs disabled, software events follow different callchains that may only disable preemption. This asymmetry in interrupt handling creates the race window.

The kernel must ensure atomic execution of the overflow handler by disabling IRQs across all callchains, preventing perf_event_exit_event() from interleaving its cleanup operations with the overflow processing.

Attack Vector

The vulnerability requires local access to trigger the race condition. An attacker would need to:

1. Create software-based perf events with attached BPF programs
2. Trigger high-frequency overflow events to maximize the race window
3. Simultaneously trigger event removal or process exit to invoke perf_remove_from_context()
4. Exploit the resulting use-after-free condition

The attack complexity is high due to the timing-dependent nature of race conditions, but successful exploitation could lead to kernel memory corruption or privilege escalation.

Detection Methods for CVE-2026-23271

Indicators of Compromise

• Kernel panic messages referencing __perf_event_overflow or perf_remove_from_context
• Unexpected BPF program crashes or errors during perf event handling
• System instability when running performance monitoring tools
• KASAN (Kernel Address Sanitizer) reports indicating use-after-free in perf subsystem

Detection Strategies

• Monitor kernel logs for oops/panic messages involving the perf subsystem functions
• Enable KASAN in development/test environments to detect memory safety violations
• Audit systems for unusual perf event activity patterns that could indicate exploitation attempts
• Deploy kernel-level monitoring for race condition detection in the perf subsystem

Monitoring Recommendations

• Implement continuous kernel log monitoring for perf-related errors
• Use system tracing tools to detect abnormal perf event lifecycle patterns
• Monitor for process crashes associated with BPF program execution in perf contexts

How to Mitigate CVE-2026-23271

Immediate Actions Required

• Apply the kernel patches from the official Linux kernel stable branches immediately
• Restrict access to the perf subsystem using perf_event_paranoid sysctl settings
• Limit BPF program attachment to perf events to trusted users only
• Consider disabling software perf events in high-security environments until patched

Patch Information

The Linux kernel maintainers have released patches across multiple stable kernel branches to address this vulnerability. The fix ensures that __perf_event_overflow() runs with IRQs disabled for all possible callchains, eliminating the race window.

Patches are available from the following kernel git commits:

• Kernel Git Commit 3f89b61
• Kernel Git Commit 4df1a45
• Kernel Git Commit 4f8d581
• Kernel Git Commit 5c48fdc
• Kernel Git Commit bb19062
• Kernel Git Commit c9bc175

Workarounds

• Increase the perf_event_paranoid sysctl value to restrict perf event access
• Disable software-based perf events if not required for operations
• Limit user access to perf_event_open() system call via seccomp or other sandboxing mechanisms
• Monitor and audit BPF program usage in conjunction with perf events

# Configuration example
# Restrict perf event access to root only
echo 3 > /proc/sys/kernel/perf_event_paranoid

# Verify the setting
cat /proc/sys/kernel/perf_event_paranoid