CVE-2026-23064: Linux Kernel Use-After-Free Vulnerability

CVE-2026-23064 Overview

A NULL pointer dereference vulnerability has been identified in the Linux kernel's traffic control (tc) subsystem, specifically within the act_ife module. The vulnerability exists in the tcf_ife_encode() function, which fails to properly validate the return value of ife_encode() before use. When ife_encode() returns NULL, subsequent operations attempt to dereference this invalid pointer, leading to a kernel crash.

This vulnerability was discovered through the syzbot automated fuzzing framework, which triggered a general protection fault when processing specially crafted network traffic through the IFE (Inter-Frame Encoding) action in the traffic control subsystem.

Critical Impact

Successful exploitation of this vulnerability can cause kernel panic and system crash, resulting in denial of service conditions on affected Linux systems utilizing the traffic control IFE action.

Affected Products

• Linux kernel with net/sched/act_ife module enabled
• Systems using traffic control (tc) IFE actions for packet encapsulation
• Network infrastructure devices running affected kernel versions

Discovery Timeline

• 2026-02-04 - CVE CVE-2026-23064 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-23064

Vulnerability Analysis

The vulnerability resides in the Linux kernel's traffic control framework within the net/sched/act_ife.c file. The IFE (Inter-Frame Encoding) action is used in the kernel's packet scheduling infrastructure to encode metadata into network packets. The flaw manifests when the tcf_ife_encode() function calls ife_encode() without validating that the return value is non-NULL before passing it to subsequent encoding functions.

When ife_encode() fails and returns NULL, the ife_encode_meta_u32() function at line 101 of act_ife.c attempts to use this NULL pointer in ife_tlv_meta_encode(), triggering a NULL pointer dereference at line 166 of net/ife/ife.c. This causes a general protection fault in the kernel.

The crash dump shows the fault occurring during packet processing through the traffic control chain: tcf_ife_act() → tcf_ife_encode() → ife_encode_meta_u32() → ife_tlv_meta_encode().

Root Cause

The root cause is insufficient error handling in the tcf_ife_encode() function. The function assumes that ife_encode() will always return a valid pointer, but under certain conditions (such as memory allocation failures or invalid parameters), ife_encode() can return NULL. Without a proper NULL check, the code proceeds to dereference this invalid pointer.

This is a classic case of missing return value validation in kernel code, which can lead to NULL pointer dereference vulnerabilities when error conditions are not properly anticipated.

Attack Vector

An attacker with the ability to configure traffic control rules on a Linux system could potentially trigger this vulnerability by:

1. Setting up a traffic control configuration that utilizes the IFE action with specific metadata encoding parameters
2. Sending network packets through the configured qdisc (queuing discipline) that trigger the vulnerable code path
3. Causing the ife_encode() function to return NULL through resource exhaustion or specific parameter combinations

The vulnerability requires local access to configure traffic control rules or the ability to send network traffic through a system with a vulnerable tc configuration. The syzbot report indicates the crash can be triggered through the cls_matchall classifier combined with the multiq queuing discipline.

Detection Methods for CVE-2026-23064

Indicators of Compromise

• Kernel panic or system crash with stack traces containing tcf_ife_encode, ife_encode_meta_u32, or ife_tlv_meta_encode
• KASAN (Kernel Address Sanitizer) reports showing null-ptr-deref in net/ife/ife.c:166
• System logs showing general protection faults originating from the traffic control subsystem
• Unexpected system reboots on devices with IFE traffic control actions configured

Detection Strategies

• Monitor kernel logs for KASAN null pointer dereference reports in the IFE module
• Deploy kernel crash dump analysis to identify crashes originating from act_ife.c code paths
• Audit traffic control configurations for systems using IFE actions with metadata encoding
• Implement real-time monitoring for kernel oops messages containing tcf_ife_act in the call trace

Monitoring Recommendations

• Enable kernel crash dump collection (kdump) to capture detailed information if the vulnerability is triggered
• Configure centralized logging to aggregate kernel messages from affected systems
• Set up alerts for sudden system reboots or kernel panic events on network infrastructure
• Review traffic control configurations periodically to identify potentially vulnerable setups

How to Mitigate CVE-2026-23064

Immediate Actions Required

• Update the Linux kernel to a patched version containing the fix commits
• If immediate patching is not possible, consider disabling or removing IFE actions from traffic control configurations
• Review and audit existing traffic control rules for IFE action usage
• Implement system monitoring to detect exploitation attempts

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix ensures that tcf_ife_encode() properly validates the return value of ife_encode() before proceeding with metadata encoding operations. The patches are available through the stable kernel git repository:

• Kernel Git Commit 03710ce
• Kernel Git Commit 27880b0
• Kernel Git Commit 374915d
• Kernel Git Commit 6c75fed

System administrators should update their kernel to a version containing these fixes. Check with your Linux distribution vendor for updated kernel packages.

Workarounds

• Remove or disable IFE actions from traffic control configurations using tc actions del action ife
• Unload the act_ife kernel module if not required: modprobe -r act_ife
• Blacklist the act_ife module to prevent automatic loading by adding blacklist act_ife to /etc/modprobe.d/blacklist.conf
• Implement network segmentation to limit access to systems that must maintain vulnerable configurations until patches can be applied

# Configuration example
# Check if act_ife module is loaded
lsmod | grep act_ife

# Remove IFE actions from traffic control (if configured)
tc actions flush action ife

# Blacklist the module to prevent loading
echo "blacklist act_ife" >> /etc/modprobe.d/blacklist-ife.conf

# Unload the module if currently loaded
modprobe -r act_ife