CVE-2026-23411: Linux Kernel Race Condition Vulnerability

CVE-2026-23411 Overview

CVE-2026-23411 is a race condition vulnerability in the Linux kernel's AppArmor security module. The flaw exists because AppArmor released the reference to i_private data immediately after removing the original entry from the filesystem. However, the inode can outlive that removal, allowing filesystem callbacks to access freed data. This creates a race between data deallocation and filesystem access paths. The rawdata/loaddata paths are the most likely candidates to lose the race, but crafted conditions could trigger races for other types stored in i_private. The issue is tracked under [CWE-362] (Concurrent Execution using Shared Resource with Improper Synchronization).

Critical Impact
A local authenticated attacker can trigger a use-after-free condition in the AppArmor subsystem, potentially leading to kernel memory corruption, information disclosure, or privilege escalation.

Affected Products

Linux Kernel (multiple stable branches, including 4.13 and 7.0 release candidates rc1 through rc7)
Distributions shipping AppArmor with vulnerable kernel versions
Any system enforcing AppArmor profiles via filesystem-exposed policy data

Discovery Timeline

2026-04-01 - CVE-2026-23411 published to NVD
2026-04-24 - Last updated in NVD database

Technical Details for CVE-2026-23411

Vulnerability Analysis

The vulnerability resides in AppArmor's management of i_private data attached to securityfs inodes. AppArmor stores policy-related structures, such as rawdata and loaddata, in the inode's private pointer. When a profile entry is removed from the filesystem, AppArmor decremented the reference count on the i_private data at the removal site. The inode itself, however, can persist beyond the entry removal because filesystem operations may still hold references to it.

During this persistence window, filesystem callback functions can dereference i_private after the underlying data has already been freed. This creates a classic time-of-use mismatch between deallocation and access. Because the kernel slab allocator may quickly reuse the freed memory, callbacks can read attacker-influenced data or trigger memory corruption. Successful exploitation can compromise kernel integrity and confidentiality.

Root Cause

The root cause is incorrect lifecycle management of i_private-referenced data. AppArmor released the reference at filesystem entry removal time rather than during inode eviction. Because inode lifetime is independent from entry removal, callback functions could execute after the reference had been dropped. The upstream fix moves the put of i_private data to the inode eviction handler, ensuring the data outlives every possible filesystem access.

Attack Vector

The attack vector is local. An authenticated user with the ability to interact with the AppArmor securityfs interface can craft sequences of policy load, unload, and read operations to race entry removal against ongoing filesystem callbacks. Exploitation requires precise timing to hit the window between reference release and callback dereference. While rawdata/loaddata are the most accessible targets, other i_private types may also be reachable with sufficient setup.

No public proof-of-concept exploit is currently available, and the EPSS data indicates low predicted exploitation likelihood. The vulnerability is described in the upstream commits referenced in the Linux kernel stable tree.

Detection Methods for CVE-2026-23411

Indicators of Compromise

Kernel oops, panic, or KASAN reports referencing AppArmor functions and i_private access after free
Unexpected crashes in aafs (AppArmor securityfs) read or release paths under concurrent policy load/unload
Kernel logs showing slab-use-after-free warnings tied to AppArmor loaddata or rawdata structures

Detection Strategies

Enable KASAN (Kernel Address Sanitizer) on test or canary hosts to catch use-after-free conditions in AppArmor code paths
Monitor audit logs for unusual frequency of AppArmor profile replace, remove, and read operations from non-administrative users
Correlate kernel crash dumps with workloads that repeatedly load and unload AppArmor profiles

Monitoring Recommendations

Track access patterns to /sys/kernel/security/apparmor/policy/ and similar securityfs paths
Alert on processes invoking apparmor_parser or policy management syscalls outside of expected configuration management windows
Centralize kernel ring buffer and dmesg output for offline analysis of race-related faults

How to Mitigate CVE-2026-23411

Immediate Actions Required

Identify all Linux hosts running kernels with AppArmor enabled and inventory their kernel versions
Apply the stable kernel updates that include the AppArmor i_private eviction fix from upstream commits
Restrict access to AppArmor securityfs interfaces to administrative users and trusted automation only
Reboot affected systems after patching to load the corrected kernel image

Patch Information

The Linux kernel maintainers released the fix across multiple stable branches. The corrective change moves the release of i_private-referenced data into the inode eviction handler, ensuring data outlives all filesystem callbacks. Patch commits are available in the kernel stable tree, including commit 13bc2772414, commit 2a732ed26f, commit 3ddb961d29, commit 667df93769, commit 8e135b8aee, commit a92c5e5086, commit ae10787d95, and commit eecce02639. Apply vendor-provided kernel updates from your Linux distribution as soon as they become available.

Workarounds

Limit local shell access on multi-tenant systems to reduce the population of users able to trigger the race
Where AppArmor is not required, evaluate disabling it via apparmor=0 on the kernel command line as a temporary measure until patches are deployed
Avoid running untrusted code with the capability to manipulate AppArmor policy or access securityfs entries

bash

# Configuration example
# Verify current kernel version
uname -r

# Check if AppArmor is enabled
cat /sys/module/apparmor/parameters/enabled

# After patching, confirm the kernel package is updated (Debian/Ubuntu)
dpkg -l | grep linux-image

# After patching, confirm the kernel package is updated (RHEL/Fedora)
rpm -q kernel

# Reboot to activate the patched kernel
sudo systemctl reboot