CVE-2024-26808: Linux Kernel Privilege Escalation Flaw

CVE-2024-26808 Overview

CVE-2024-26808 is a vulnerability in the Linux kernel's netfilter subsystem, specifically within the nft_chain_filter module. The flaw occurs when a network device is unregistered but its reference remains in the inet/ingress basechain hook list, creating a stale reference condition. This can lead to system instability and denial of service conditions when the kernel attempts to access the invalid netdevice reference.

Critical Impact

Local attackers with low privileges can exploit this vulnerability to cause denial of service through kernel crashes by triggering stale netdevice references in netfilter hook lists.

Affected Products

• Linux Kernel (multiple versions including 6.8-rc1)
• Debian Linux 10.0
• Systems using netfilter with inet/ingress basechains

Discovery Timeline

• April 4, 2024 - CVE-2024-26808 published to NVD
• April 4, 2025 - Last updated in NVD database

Technical Details for CVE-2024-26808

Vulnerability Analysis

This vulnerability exists in the Linux kernel's netfilter framework, which provides packet filtering, network address translation, and port translation functionality. The issue specifically affects the nft_chain_filter component responsible for managing filter chains in the nftables subsystem.

When a network device is removed from the system (triggering a NETDEV_UNREGISTER event), the kernel's netfilter code fails to properly remove the netdevice reference from inet/ingress basechain hook lists. This oversight results in dangling pointers that remain in the hook list even after the associated network device has been deallocated.

The vulnerability requires local access to exploit but only needs low privileges, making it accessible to authenticated users on affected systems. Successful exploitation results in denial of service, potentially causing kernel panics or system crashes when the stale reference is dereferenced.

Root Cause

The root cause is improper handling of the NETDEV_UNREGISTER event notification in the nft_chain_filter module. When a network interface is unregistered, the module fails to clean up references to the netdevice from inet/ingress basechains. This creates a use-after-free scenario where the kernel maintains pointers to memory that may be reallocated for other purposes, leading to memory corruption or crashes.

Attack Vector

The attack vector requires local access to the system. An attacker with low privileges can trigger the vulnerability by manipulating network interfaces in conjunction with nftables rules using inet/ingress basechains. The attack does not require user interaction and the scope is unchanged, meaning the impact is limited to the vulnerable component itself.

Exploitation involves creating nftables rules attached to a network device using inet family ingress chains, then triggering the device's removal while the hook remains registered. The resulting stale reference can cause the kernel to crash when processing network packets or during hook traversal operations.

Detection Methods for CVE-2024-26808

Indicators of Compromise

• Unexpected kernel panics or oops messages referencing netfilter or nft_chain_filter
• System crashes occurring during network interface removal or reconfiguration
• Kernel log messages indicating invalid memory access in netfilter subsystem
• Core dumps showing netfilter-related stack traces

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for netfilter-related errors and warnings
• Implement kernel crash dump analysis to identify exploitation patterns
• Use kernel debugging tools to track netdevice reference counting anomalies
• Deploy system monitoring to detect unusual network interface manipulation patterns

Monitoring Recommendations

• Enable kernel crash dump collection for post-incident analysis
• Configure alerting for kernel panic events on affected systems
• Monitor for suspicious processes repeatedly adding/removing network interfaces
• Track nftables rule modifications, especially those involving inet/ingress chains

How to Mitigate CVE-2024-26808

Immediate Actions Required

• Update Linux kernel to a patched version immediately
• Review and audit nftables configurations using inet/ingress basechains
• Restrict local user access on critical systems until patches are applied
• Monitor systems for signs of exploitation or instability

Patch Information

Multiple patches have been released to address this vulnerability. The fix properly handles the NETDEV_UNREGISTER event by removing the netdevice reference from inet/ingress basechains before the device is deallocated. Patches are available from the official Linux kernel Git repository:

• Linux Kernel Patch
• Linux Kernel Update
• Linux Kernel Security Commit
• Linux Kernel Fix
• Linux Kernel Improvement
• Linux Kernel Change Log

Debian users should refer to the Debian LTS Announcement for distribution-specific updates.

Workarounds

• Avoid using inet family ingress chains until patches can be applied
• Minimize network interface changes on systems with nftables inet/ingress rules
• Implement strict access controls to limit local user capabilities
• Consider using iptables as an alternative to nftables on unpatched systems

# Check current kernel version
uname -r

# List nftables rules to identify inet/ingress chains
nft list ruleset | grep -E "inet.*ingress"

# Update kernel on Debian-based systems
apt update && apt upgrade linux-image-$(uname -r)

# Verify patch is applied by checking kernel version
dpkg -l | grep linux-image