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 IMA handles a dentry's d_name.name field, which can change during a rename operation while the earlier value is freed. None of the required synchronization primitives (d_lock, parent d_lock, exclusive i_rwsem on the parent inode, or rename_lock) are held at the affected sites. The fix takes a stable snapshot of the name instead of referencing the volatile pointer. The issue is classified under [CWE-416] Use After Free and affects mainline Linux kernel builds along with Debian Linux distributions.
Critical Impact
A local authenticated attacker can trigger memory corruption in kernel context, potentially leading to privilege escalation, kernel information disclosure, or denial of service.
Affected Products
- Linux Kernel (multiple stable branches prior to the fix commits)
- Debian Linux 11.0 (Bullseye)
- Systems with IMA (Integrity Measurement Architecture) enabled
Discovery Timeline
- 2024-07-12 - CVE-2024-39494 published to NVD
- 2025-01 - Debian LTS security advisory issued
- 2025-05 - Additional Debian LTS advisory issued
- 2026-01-06 - Last updated in NVD database
Technical Details for CVE-2024-39494
Vulnerability Analysis
The vulnerability resides in the Linux kernel's IMA subsystem, which measures and appraises file integrity for security policy enforcement. IMA accesses a dentry's ->d_name.name field to identify files during measurement operations. The Virtual File System (VFS) layer allows ->d_name.name to change during rename operations, and the original buffer can be freed concurrently.
Proper stabilization of this pointer requires one of several locks: ->d_lock on the dentry, ->d_lock on its parent, exclusive ->i_rwsem on the parent's inode, or the global rename_lock. The affected IMA code paths held none of these locks while dereferencing ->d_name.name, creating a classic use-after-free condition.
Root Cause
The root cause is missing synchronization between IMA's read access to d_name.name and concurrent VFS rename operations. When a rename frees the original name buffer, IMA may continue to read freed memory, producing undefined behavior in kernel space. The fix replaces direct pointer access with a stable snapshot of the name string.
Attack Vector
Exploitation requires local access with low privileges. An attacker who can trigger file operations measured by IMA while concurrently renaming files can race the kernel into dereferencing freed memory. Successful exploitation may lead to kernel memory corruption, leak of sensitive kernel data, or escalation to root privileges. The bug is not known to be exploited in the wild and is not listed in the CISA Known Exploited Vulnerabilities catalog.
No public proof-of-concept is available. See the upstream commits such as Linux Kernel Commit edf287b for the technical fix.
Detection Methods for CVE-2024-39494
Indicators of Compromise
- Unexpected kernel oops or panic messages referencing IMA functions or dentry name handling in dmesg or /var/log/kern.log.
- KASAN (Kernel Address Sanitizer) reports flagging use-after-free in IMA code paths on instrumented kernels.
- Anomalous process privilege transitions following heavy file rename activity on IMA-enabled systems.
Detection Strategies
- Compare installed kernel package versions against the fixed commits listed in the Debian LTS advisories and upstream stable branches.
- Monitor for processes performing high-frequency rename operations on files under IMA measurement policy, particularly from unprivileged user contexts.
- Audit IMA policy configuration to identify systems where the vulnerable code paths are reachable.
Monitoring Recommendations
- Enable kernel audit logging for rename, renameat, and renameat2 syscalls correlated with IMA measurement events.
- Track kernel crash telemetry across the fleet to surface clusters of IMA-related faults.
- Forward kernel logs to a centralized SIEM for correlation against process execution and privilege escalation events.
How to Mitigate CVE-2024-39494
Immediate Actions Required
- Apply the Linux kernel updates from your distribution that include the upstream fix commits referenced by the Debian LTS Announcement January 2025 and Debian LTS Announcement May 2025.
- Reboot affected systems after package upgrades to load the patched kernel.
- Inventory IMA-enabled hosts and prioritize them for patching, as they expose the vulnerable code paths.
Patch Information
The upstream Linux kernel fix is distributed across multiple stable branches in commits edf287bc, 0b31e28f, 480afcbe, 7fb37498, a78a6f0d, be84f32b, and dd431c3a. Debian users should upgrade to the kernel versions specified in the Debian LTS advisories. Full commit details are available at Linux Kernel Commit dd431c3 and the related upstream references.
Workarounds
- If patching cannot be performed immediately, disable IMA measurement on non-essential systems by removing or restricting the IMA policy in /etc/ima/ima-policy.
- Restrict local user access on IMA-enabled hosts to reduce the attack surface for local privilege escalation.
- Apply strict mount options and file access controls to limit untrusted users' ability to trigger rename operations on measured files.
# Verify installed kernel version against fixed releases
uname -r
dpkg -l | grep linux-image
# Apply Debian security updates
sudo apt update
sudo apt upgrade linux-image-$(uname -r | cut -d- -f3-)
sudo reboot
# Optional: review active IMA policy
sudo cat /sys/kernel/security/ima/policy
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
