CVE-2024-23848: Linux Kernel Use-After-Free Vulnerability

CVE-2024-23848 Overview

CVE-2024-23848 is a use-after-free vulnerability [CWE-416] in the Linux kernel through version 6.7.1. The flaw resides in the cec_queue_msg_fh function within the Consumer Electronics Control (CEC) subsystem, specifically in drivers/media/cec/core/cec-adap.c and drivers/media/cec/core/cec-api.c. A local authenticated user can trigger the use-after-free condition to cause a denial of service through kernel memory corruption. The vulnerability affects systems where the CEC media driver is loaded and accessible to unprivileged users.

Critical Impact
Local low-privileged users can trigger kernel memory corruption in the CEC subsystem, leading to system crashes and denial of service on affected Linux hosts.

Affected Products

Linux Kernel versions up to and including 6.7.1
Distributions shipping vulnerable kernels with CEC media drivers enabled
Siemens industrial products bundling affected kernel versions (per Siemens advisory SSA-265688)

Discovery Timeline

2024-01-23 - CVE-2024-23848 published to the National Vulnerability Database
2026-05-12 - Last updated in NVD database

Technical Details for CVE-2024-23848

Vulnerability Analysis

The vulnerability is a use-after-free condition [CWE-416] in the Linux kernel's CEC core driver. The cec_queue_msg_fh function handles queueing of CEC messages to file handle structures used by userspace consumers of the CEC API. Improper lifetime management of these structures allows the kernel to dereference memory that has already been freed.

The attack requires local access with low privileges and no user interaction. Successful exploitation impacts availability through kernel crashes, while confidentiality and integrity are not directly affected per the CVSS vector. The CEC subsystem exposes character devices under /dev/cec*, which are the entry points an attacker uses to invoke the vulnerable code paths.

Root Cause

The root cause lies in race conditions between message queueing and file handle teardown in the CEC adapter code. When a CEC file handle is released concurrently with cec_queue_msg_fh enqueueing a message, the queue operation can reference a freed struct cec_fh. The patched code corrects the reference counting and synchronization around the file handle lifetime in drivers/media/cec/core/cec-adap.c and drivers/media/cec/core/cec-api.c.

Attack Vector

Exploitation is local. An attacker with shell access and permission to open /dev/cec* devices issues concurrent ioctl operations and close operations against the CEC device. The resulting race triggers the use-after-free during message queueing. See the Kernel Mailing List Discussion for the upstream technical analysis.

No verified public proof-of-concept code is available. Refer to the upstream kernel discussion for technical details on the affected code paths.

Detection Methods for CVE-2024-23848

Indicators of Compromise

Unexpected kernel oops or panic messages referencing cec_queue_msg_fh, cec-adap.c, or cec-api.c in dmesg or /var/log/kern.log
KASAN (Kernel Address Sanitizer) reports identifying use-after-free conditions in the CEC subsystem on instrumented kernels
Repeated process crashes or system instability correlated with access to /dev/cec* devices

Detection Strategies

Inventory running kernel versions across Linux endpoints and flag hosts running kernel 6.7.1 or earlier without the upstream CEC fix backported
Monitor for unprivileged processes opening /dev/cec* character devices, which is unusual outside of media applications
Correlate kernel ring buffer messages with process activity to identify users triggering CEC ioctl sequences immediately before crashes

Monitoring Recommendations

Forward dmesg and /var/log/kern.log to a centralized logging platform and alert on kernel oops signatures involving CEC functions
Audit auditd rules covering open syscalls against /dev/cec* paths and review activity from non-media service accounts
Track kernel package versions through configuration management to confirm patch deployment status across the fleet

How to Mitigate CVE-2024-23848

Immediate Actions Required

Update the Linux kernel to a version that includes the upstream fix for the cec_queue_msg_fh use-after-free, beyond 6.7.1
Apply distribution-provided kernel security updates from your vendor (Red Hat, SUSE, Debian, Ubuntu, etc.) once available
For Siemens industrial products, follow the remediation guidance in Siemens Security Advisory SSA-265688
Restrict access to /dev/cec* devices to trusted users and services only

Patch Information

The upstream fix is tracked through the Linux kernel mailing list. Review the Kernel Mailing List Discussion for the patch series addressing the use-after-free in the CEC adapter and API code. Deploy the kernel update through your standard package management workflow and reboot affected systems to load the patched kernel.

Workarounds

Unload the cec kernel module on systems that do not require Consumer Electronics Control functionality using modprobe -r cec
Blacklist the CEC module by adding blacklist cec to /etc/modprobe.d/blacklist-cec.conf to prevent automatic loading at boot
Tighten permissions on /dev/cec* device nodes through udev rules so only privileged accounts can open them

bash

# Blacklist the CEC module to prevent loading on systems that do not need it
echo "blacklist cec" | sudo tee /etc/modprobe.d/blacklist-cec.conf
sudo modprobe -r cec 2>/dev/null || true

# Verify the module is not loaded
lsmod | grep -E '^cec'

# Restrict access to CEC device nodes via udev (example rule)
echo 'KERNEL=="cec[0-9]*", MODE="0600", OWNER="root"' | \
  sudo tee /etc/udev/rules.d/90-cec-restrict.rules
sudo udevadm control --reload-rules && sudo udevadm trigger