CVE-2024-27043: Linux Kernel Use-After-Free Vulnerability

CVE-2024-27043 Overview

CVE-2024-27043 is a use-after-free vulnerability in the Linux kernel's DVB (Digital Video Broadcasting) device subsystem. The flaw exists in the dvb_register_device function where a pointer (*pdvbdev) is set equal to dvbdev, which gets freed in several error-handling paths. However, the pointer is not set to NULL after deallocation, leading to use-after-free conditions when subsequent functions attempt to access the already-freed memory.

Critical Impact

Local attackers with low privileges can exploit this memory corruption vulnerability to potentially achieve arbitrary code execution or cause system instability through improper memory access.

Affected Products

• Linux Kernel (multiple versions)
• Debian Linux (LTS releases)
• Systems utilizing DVB media subsystem functionality

Discovery Timeline

• May 1, 2024 - CVE-2024-27043 published to NVD
• December 23, 2024 - Last updated in NVD database

Technical Details for CVE-2024-27043

Vulnerability Analysis

This use-after-free vulnerability occurs in the DVB device registration subsystem of the Linux kernel. The root issue manifests in the dvb_register_device function where memory management is improperly handled during error conditions. When an error occurs during device registration, the dvbdev structure is freed, but the pointer stored in *pdvbdev continues to reference the deallocated memory location.

The vulnerability can be triggered through a specific call chain involving budget_register → dvb_dmxdev_init → dvb_register_device → dvb_dmxdev_release → dvb_unregister_device → dvb_remove_device → dvb_device_put → kref_put. When dvb_unregister_device is called, it operates on dmxdev->dvbdev which may point to memory that was already freed in the earlier dvb_register_device call, triggering the use-after-free condition.

Root Cause

The root cause is a failure to properly nullify the *pdvbdev pointer after the dvbdev structure is deallocated in error-handling paths within dvb_register_device. This is a classic dangling pointer issue where the pointer continues to hold a reference to freed memory, allowing subsequent code paths to dereference invalid memory.

Attack Vector

This vulnerability requires local access to the system with low privileges. An attacker would need to trigger the specific error conditions in the DVB device registration process and then invoke the cleanup path that attempts to access the freed memory. The attack does not require user interaction and operates within the kernel's memory space, potentially allowing privilege escalation or system crashes.

The exploitation flow follows the DVB device lifecycle:

1. Device registration initiates via budget_register
2. Error condition triggers memory deallocation in dvb_register_device
3. Pointer remains valid but points to freed memory
4. Cleanup routines access the dangling pointer
5. Use-after-free occurs in kref_put operations

Detection Methods for CVE-2024-27043

Indicators of Compromise

• Unexpected kernel panics or crashes related to the DVB subsystem
• Kernel oops messages referencing dvb_register_device, dvb_unregister_device, or kref_put functions
• Memory corruption signatures in kernel logs involving media/dvb components

Detection Strategies

• Monitor kernel logs for KASAN (Kernel Address Sanitizer) reports indicating use-after-free in DVB-related functions
• Deploy kernel debugging tools to detect invalid memory access patterns in the media subsystem
• Utilize SentinelOne's kernel-level behavioral monitoring to identify anomalous memory operations

Monitoring Recommendations

• Enable kernel memory debugging features such as KASAN or KFENCE to detect memory corruption
• Configure system logging to capture detailed kernel messages from the media/dvb subsystem
• Implement real-time monitoring for kernel module loading and device registration events

How to Mitigate CVE-2024-27043

Immediate Actions Required

• Update the Linux kernel to a patched version immediately
• Review systems using DVB media devices for signs of exploitation
• Consider temporarily disabling DVB functionality if patches cannot be immediately applied
• Apply vendor-specific patches from your distribution's security advisories

Patch Information

The Linux kernel maintainers have released patches across multiple stable kernel branches. The fix ensures that *pdvbdev is set to NULL after the dvbdev structure is freed in error-handling paths, preventing subsequent code from accessing deallocated memory.

Patches are available through the following resources:

• Linux Kernel Stable Commit 096237039d00
• Linux Kernel Stable Commit 8c64f4cdf4e6
• Linux Kernel Stable Commit 779e8db7efb2
• Debian LTS Security Advisory

Workarounds

• Disable or blacklist DVB-related kernel modules if not required for system operation
• Implement strict access controls to limit which users can interact with DVB devices
• Deploy SentinelOne endpoint protection to monitor for exploitation attempts targeting this vulnerability

# Temporarily disable DVB modules (if not required)
echo "blacklist dvb_core" >> /etc/modprobe.d/blacklist-dvb.conf
echo "blacklist dvb_usb" >> /etc/modprobe.d/blacklist-dvb.conf
# Unload currently loaded DVB modules
modprobe -r dvb_usb dvb_core 2>/dev/null || true
# Verify modules are not loaded
lsmod | grep dvb