CVE-2026-23410: Linux Kernel Race Condition Vulnerability

CVE-2026-23410 Overview

CVE-2026-23410 is a use-after-free vulnerability in the Linux kernel's AppArmor security module caused by a race condition in the handling of rawdata inodes. The vulnerability exists because rawdata inodes are not properly reference-counted, allowing an attacker to trigger a use-after-free condition by simultaneously opening a rawdata file while removing the last reference to the associated profile data. When the profile is removed, the struct aa_loaddata is freed, leaving i_private as a dangling pointer that is subsequently dereferenced in seq_rawdata_open(), resulting in access to freed memory.

Critical Impact

Local attackers with low privileges can exploit this race condition to achieve arbitrary code execution with elevated privileges, potentially gaining complete control over the affected system.

Affected Products

• Linux Kernel (multiple versions with AppArmor enabled)
• Linux distributions using vulnerable kernel versions with AppArmor security module
• Systems with AppArmor policy management enabled

Discovery Timeline

• 2026-04-01 - CVE-2026-23410 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-23410

Vulnerability Analysis

This vulnerability is a classic Time-of-Check Time-of-Use (TOCTOU) race condition leading to a use-after-free memory corruption scenario. The flaw exists in the AppArmor subsystem's handling of rawdata files exposed through the virtual filesystem interface.

The core issue stems from a design decision to avoid circular reference counts between profiles and their associated rawdata inodes. While profiles hold references to rawdata, the inodes themselves lack proper refcounting, creating a window during profile removal where the VFS layer and profile destruction can race.

When an attacker opens a rawdata file (triggering VFS operations) while simultaneously removing the associated AppArmor profile (through policy management), the following sequence can occur:

1. The attacker initiates an open() system call on a rawdata file
2. Concurrently, the last profile reference to the rawdata is removed
3. The struct aa_loaddata structure is freed
4. The VFS layer continues processing and reaches seq_rawdata_open()
5. The function dereferences i_private, which now points to freed memory

Successful exploitation allows attackers to read or write to freed kernel memory, potentially leading to arbitrary code execution in kernel context.

Root Cause

The root cause is the lack of proper reference counting on rawdata inodes in the AppArmor security module. The original design attempted to avoid circular reference dependencies by having profiles hold the rawdata reference rather than the inodes themselves. However, this approach failed to account for the race window between VFS operations and profile destruction, leaving the rawdata accessible via i_private after the backing memory was freed.

Attack Vector

The attack requires local access to the system with low privileges. An attacker must have the ability to interact with AppArmor rawdata files (typically exposed in /sys/kernel/security/apparmor/) and the capability to trigger profile removal or modification. The attack exploits the race window between file operations and profile management to access freed memory.

The attack involves timing-sensitive operations:

• Initiating file operations on AppArmor rawdata entries
• Triggering profile removal to free the associated aa_loaddata structure
• Winning the race to have the VFS layer access the freed memory

This can potentially be achieved through normal user-space operations if the attacker has appropriate permissions to both read rawdata files and manage AppArmor profiles, or through exploiting other privilege escalation vectors to gain these capabilities.

Detection Methods for CVE-2026-23410

Indicators of Compromise

• Kernel crash logs or oops messages referencing seq_rawdata_open() or AppArmor rawdata handling functions
• Unexpected system instability or crashes during AppArmor profile management operations
• Evidence of repeated rapid AppArmor profile loading and unloading operations
• Memory corruption indicators in kernel memory allocation debugging output (KASAN reports)

Detection Strategies

• Enable Kernel Address Sanitizer (KASAN) to detect use-after-free memory access in kernel space
• Monitor for suspicious patterns of AppArmor profile modifications combined with rawdata file access
• Deploy SentinelOne Singularity Platform for real-time kernel-level threat detection and behavioral analysis
• Implement auditd rules to track access to /sys/kernel/security/apparmor/ filesystem entries

Monitoring Recommendations

• Configure kernel crash dump collection (kdump) to capture diagnostic information if exploitation is attempted
• Enable AppArmor audit logging to track profile loading, modification, and removal events
• Monitor system logs for AppArmor-related error messages or warnings indicating potential race conditions
• Deploy endpoint detection solutions capable of identifying kernel exploitation attempts and privilege escalation

How to Mitigate CVE-2026-23410

Immediate Actions Required

• Apply the latest kernel security patches from your Linux distribution immediately
• Restrict access to AppArmor management interfaces to only trusted administrative accounts
• Consider temporarily disabling AppArmor rawdata file exposure if patches are not immediately available
• Audit systems for signs of exploitation attempts before and after patching

Patch Information

The Linux kernel maintainers have addressed this vulnerability by implementing a double reference counting scheme. The fix separates the profile refcount from the inode reference management, allowing the rawdata to be properly freed only after all inode references are released.

Multiple kernel patches have been released to address this issue:

• Kernel Patch 6ef1f29
• Kernel Patch 763e838
• Kernel Patch a0b7091
• Kernel Patch af782cc
• Kernel Patch f9761ad

Contact your Linux distribution vendor for the appropriate patched kernel package.

Workarounds

• Restrict access to AppArmor management capabilities using Linux capabilities or SELinux/AppArmor policies
• Limit local user access to systems where AppArmor profile management is required
• Implement strict separation of duties for systems requiring AppArmor configuration changes
• Consider using container isolation to limit exposure of AppArmor interfaces to untrusted processes

# Restrict access to AppArmor security filesystem
chmod 700 /sys/kernel/security/apparmor/
# Alternatively, mount with restrictive permissions
mount -o remount,mode=700 /sys/kernel/security/