CVE-2024-39494: Linux Kernel Use-After-Free Vulnerability

CVE-2024-39494 Overview

CVE-2024-39494 is a use-after-free vulnerability in the Linux kernel's Integrity Measurement Architecture (IMA) subsystem. The flaw exists in how the kernel handles a dentry's dname.name field, which can change during a rename operation, leading to access of freed memory. The vulnerability arises because the ->d_name.name pointer can be freed after a rename operation while still being referenced elsewhere in the code, and none of the required synchronization mechanisms (->d_lock on dentry, ->d_lock on parent, ->i_rwsem exclusive on parent's inode, or rename_lock) are properly held at the affected code sites.

Critical Impact

Local attackers with low privileges can exploit this use-after-free condition to potentially achieve arbitrary code execution, information disclosure, or denial of service on affected Linux systems.

Affected Products

• Linux Kernel (multiple versions)
• Debian Linux 11.0
• Linux-based distributions using vulnerable kernel versions

Discovery Timeline

• 2024-07-12 - CVE-2024-39494 published to NVD
• 2026-01-06 - Last updated in NVD database

Technical Details for CVE-2024-39494

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption flaw that occurs when a program continues to use a pointer after the memory it references has been deallocated. In this specific case, the IMA subsystem accesses the ->d_name.name field of a dentry structure without proper synchronization, creating a race condition during file rename operations.

The Linux kernel's dentry (directory entry) cache maintains filename information that can be modified during rename operations. When a file is renamed, the original d_name.name value may be freed while the IMA code still holds a reference to it. Subsequent access to this freed memory can lead to undefined behavior, including potential code execution if an attacker can control the contents of the reallocated memory.

Root Cause

The root cause of this vulnerability is the lack of proper locking when accessing the ->d_name.name field in the IMA subsystem. The kernel documentation specifies that to safely access this field, one of the following conditions must be met: holding ->d_lock on the dentry, holding ->d_lock on its parent, holding ->i_rwsem exclusive on the parent's inode, or holding rename_lock. However, none of these synchronization mechanisms were being used at the vulnerable code sites.

The fix involves taking a stable snapshot of the name instead of directly referencing the dentry's name field, ensuring that even if the original name is freed during a concurrent rename operation, the IMA code operates on its own copy.

Attack Vector

This is a local attack vector requiring the attacker to have low-privilege access to the system. The attacker would need to trigger a race condition between a file rename operation and IMA integrity checking on the same file. By carefully timing these operations, an attacker could cause the IMA code to access freed memory. If the attacker can control the contents of the memory that gets reallocated in place of the freed name buffer, they may be able to achieve arbitrary code execution with kernel privileges.

The attack requires local access and the ability to perform file operations on the system. While no public exploits are currently available, the vulnerability affects a core kernel subsystem present on most Linux systems.

Detection Methods for CVE-2024-39494

Indicators of Compromise

• Kernel panic or oops messages referencing IMA subsystem functions
• Unexpected kernel crashes during file operations, particularly renames
• KASAN (Kernel Address Sanitizer) reports indicating use-after-free in IMA code paths
• Anomalous system behavior when integrity measurement operations are running concurrently with file renames

Detection Strategies

• Enable KASAN in development/testing environments to detect memory corruption
• Monitor kernel logs for memory-related warnings in IMA subsystem (dmesg | grep -i ima)
• Deploy runtime kernel instrumentation to detect use-after-free conditions
• Review audit logs for unusual patterns of file rename operations combined with integrity checks

Monitoring Recommendations

• Configure syslog alerting for kernel memory corruption messages
• Implement host-based intrusion detection monitoring for kernel anomalies
• Use SentinelOne Singularity Platform's kernel-level visibility to detect exploitation attempts
• Monitor for privilege escalation attempts following unusual kernel behavior

How to Mitigate CVE-2024-39494

Immediate Actions Required

• Update to patched kernel versions as soon as possible
• Review and apply security updates from your Linux distribution vendor
• Consider temporarily disabling IMA if not required for operations (may impact security posture)
• Monitor systems for signs of exploitation while awaiting patching

Patch Information

The Linux kernel maintainers have released patches across multiple kernel stable branches. The fix takes a stable snapshot of the dentry name instead of directly referencing the potentially unstable ->d_name.name field. Patches are available through the following kernel commits:

• Kernel Commit 0b31e28
• Kernel Commit 480afcb
• Kernel Commit 7fb3749
• Kernel Commit a78a6f0
• Kernel Commit be84f32
• Kernel Commit dd431c3
• Kernel Commit edf287b

Debian users should refer to the Debian LTS Security Announcements for distribution-specific packages.

Workarounds

• Limit local access to trusted users only until patches can be applied
• Implement additional access controls to restrict file operations in sensitive directories
• Consider using kernel live patching solutions if available for your distribution
• Increase monitoring and alerting thresholds for kernel-related anomalies

# Check current kernel version and IMA status
uname -r
cat /sys/kernel/security/ima/policy 2>/dev/null || echo "IMA not mounted or accessible"

# Verify if running a patched kernel (example for checking commit)
# The specific version varies by distribution
apt list --installed 2>/dev/null | grep linux-image
# or
rpm -qa | grep kernel