CVE-2026-23408: Linux Kernel Use-After-Free Vulnerability

CVE-2026-23408 Overview

A double free vulnerability has been identified in the Linux kernel's AppArmor security module within the aa_replace_profiles() function. This memory corruption flaw occurs during the handling of namespace names when replacing security profiles, potentially allowing a local attacker with low privileges to achieve code execution, corrupt kernel memory, or cause system instability.

Critical Impact

Local attackers can exploit this double free vulnerability to potentially escalate privileges, execute arbitrary code in kernel context, or cause system crashes leading to denial of service conditions.

Affected Products

• Linux Kernel (multiple versions with AppArmor enabled)
• Systems using AppArmor mandatory access control

Discovery Timeline

• 2026-04-01 - CVE CVE-2026-23408 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-23408

Vulnerability Analysis

The vulnerability exists in the AppArmor profile replacement mechanism, specifically within the aa_replace_profiles() function. The flaw occurs due to improper memory ownership handling during namespace name assignment operations.

When aa_unpack() is called at line 1071 and results in a NULL ns_name, the code subsequently checks if ent->ns_name contains a valid namespace name at line 1089. If this condition is true, ns_name is assigned the pointer value from ent->ns_name at line 1095. However, this creates a situation where both ent->ns_name and ns_name reference the same memory allocation.

The critical error manifests when aa_load_ent_free(ent) is called at line 1262, which frees the memory pointed to by ent->ns_name. Subsequently, the code attempts to free ns_name again at line 1270 via kfree(ns_name), resulting in a double free condition since both pointers reference the same already-freed memory region.

Root Cause

The root cause is a failure to properly transfer ownership of the ns_name pointer between data structures. When ns_name is assigned from ent->ns_name, the original pointer in the entry structure should be set to NULL to prevent the subsequent double free. The fix addresses this by NULLing out ent->ns_name after the pointer value is transferred to ns_name, ensuring clear memory ownership and preventing the double free condition.

Attack Vector

This vulnerability requires local access to the system with the ability to manipulate AppArmor profiles. An attacker with low privileges could potentially trigger the vulnerable code path by crafting malicious profile replacement operations. The double free condition could be exploited through heap manipulation techniques to:

1. Corrupt kernel heap metadata, potentially leading to arbitrary write primitives
2. Achieve use-after-free conditions by reallocating the freed memory
3. Escalate privileges by manipulating critical kernel data structures

The vulnerability occurs when an unpacked profile data structure contains a namespace name while the unpacking operation returns NULL for the direct ns_name parameter, creating the aliased pointer scenario.

Detection Methods for CVE-2026-23408

Indicators of Compromise

• Unexpected kernel panics or crashes related to memory corruption in AppArmor subsystem
• Kernel log messages indicating double free detection or heap corruption
• Abnormal AppArmor profile loading or replacement operations
• KASAN (Kernel Address Sanitizer) reports showing double free in aa_replace_profiles()

Detection Strategies

• Enable KASAN and KFENCE kernel debugging features to detect double free conditions at runtime
• Monitor kernel logs for AppArmor-related error messages or memory corruption warnings
• Deploy kernel live patching solutions to detect and mitigate exploitation attempts
• Use SentinelOne Singularity platform for real-time kernel behavior monitoring

Monitoring Recommendations

• Enable kernel audit logging for AppArmor profile management operations
• Monitor for unusual privilege escalation attempts following AppArmor interactions
• Implement file integrity monitoring on AppArmor policy directories
• Track kernel memory allocation patterns for anomalies in the AppArmor subsystem

How to Mitigate CVE-2026-23408

Immediate Actions Required

• Apply the kernel patch immediately from the official kernel Git repositories
• If patching is not immediately possible, consider restricting access to AppArmor profile management
• Ensure only trusted administrators have permissions to load or replace AppArmor profiles
• Monitor systems for signs of exploitation until patches are applied

Patch Information

The Linux kernel maintainers have released fixes across multiple stable kernel branches. The patch correctly NULLs out ent->ns_name after transferring its value to ns_name, ensuring proper memory ownership and preventing the double free.

Patches are available from the following official kernel Git commits:

• Kernel Git Commit 18b5233e860c
• Kernel Git Commit 55ef2af7490a
• Kernel Git Commit 5df0c44e8f5f
• Kernel Git Commit 7998ab3010d2
• Kernel Git Commit 86feeccd6b93

Workarounds

• Restrict AppArmor profile replacement capabilities to only essential administrative accounts
• Consider temporarily disabling AppArmor if not critical to operations while awaiting patches
• Implement additional access controls to limit which users can modify AppArmor policies
• Enable kernel memory debugging features (KASAN, SLUB_DEBUG) to detect exploitation attempts

# Restrict AppArmor profile management permissions
chmod 700 /etc/apparmor.d/
chown root:root /etc/apparmor.d/

# Enable kernel memory debugging (rebuild kernel with these options)
# CONFIG_KASAN=y
# CONFIG_SLUB_DEBUG=y