CVE-2026-23412: Linux Kernel Use-After-Free Vulnerability

CVE-2026-23412 Overview

CVE-2026-23412 is a Use-After-Free vulnerability in the Linux kernel's netfilter BPF subsystem. The vulnerability occurs when concurrent processes dump hooks via nfnetlink_hooks, leading to a race condition where memory is released while readers are still accessing it. This can result in accessing freed memory (slab-use-after-free), which was detected by KASAN in the nfnl_hook_dump_one function.

Critical Impact

A local attacker could potentially exploit this Use-After-Free condition to cause system instability, denial of service, or potentially achieve privilege escalation by manipulating freed memory structures in the kernel's netfilter subsystem.

Affected Products

• Linux Kernel (multiple versions with netfilter BPF hook functionality)
• Systems utilizing nfnetlink_hooks for netfilter hook dumping
• Kernel configurations with BPF and netfilter enabled

Discovery Timeline

• April 02, 2026 - CVE-2026-23412 published to NVD
• April 02, 2026 - Last updated in NVD database

Technical Details for CVE-2026-23412

Vulnerability Analysis

This vulnerability is a classic Use-After-Free (UaF) condition in the Linux kernel's netfilter BPF hook handling code. The issue was reported by Yiming Qian and manifests when a concurrent process attempts to dump netfilter hooks via the nfnetlink_hooks interface while another process is freeing the associated hook memory.

The KASAN (Kernel Address Sanitizer) detected an invalid 8-byte read operation at address ffff888003edbf88 in the nfnl_hook_dump_one.isra.0 function, indicating that the code attempted to access memory that had already been freed and returned to the slab allocator. The call trace shows the vulnerability path through netlink_dump and nfnl_hook_get functions.

Root Cause

The root cause is improper synchronization between memory release operations and concurrent RCU (Read-Copy-Update) readers. When netfilter BPF hooks are being dumped via nfnetlink_hooks, the hook memory could be freed before all RCU readers have completed their read operations. The fix defers the memory release until after concurrent RCU readers have finished accessing the hook structures, ensuring proper memory lifecycle management.

Attack Vector

The attack vector requires local access to the system with the ability to interact with the netfilter subsystem. An attacker would need to:

1. Trigger concurrent operations on netfilter hooks - one process initiating a hook dump via nfnetlink_hooks while another process triggers hook removal
2. Exploit the race window between memory free and subsequent access
3. Potentially manipulate the freed memory to achieve code execution or privilege escalation

The vulnerability requires precise timing to exploit, as the race window is relatively small. However, kernel Use-After-Free vulnerabilities are considered serious due to their potential for privilege escalation.

Detection Methods for CVE-2026-23412

Indicators of Compromise

• KASAN alerts in kernel logs indicating slab-use-after-free in nfnl_hook_dump_one function
• Kernel panics or unexpected system crashes related to netfilter operations
• Unusual activity involving netfilter hook enumeration via netlink sockets
• Memory corruption indicators in kernel slab allocator logs

Detection Strategies

• Enable KASAN (Kernel Address Sanitizer) on development and testing systems to detect memory corruption issues
• Monitor kernel logs for netfilter-related crash dumps or memory access violations
• Implement kernel auditing for netlink socket operations involving nfnetlink_hooks
• Deploy endpoint detection tools capable of monitoring kernel-level memory anomalies

Monitoring Recommendations

• Configure system logging to capture kernel warnings and KASAN reports related to netfilter subsystem
• Set up alerts for unexpected kernel crashes or panics involving the netfilter or BPF subsystems
• Monitor for processes making unusual netlink socket calls to the netfilter subsystem
• Use SentinelOne's kernel-level behavioral monitoring to detect exploitation attempts targeting memory corruption vulnerabilities

How to Mitigate CVE-2026-23412

Immediate Actions Required

• Update the Linux kernel to a patched version containing the RCU deferral fix
• Review systems running kernels with netfilter BPF functionality enabled for potential exposure
• Consider restricting access to netfilter configuration interfaces to privileged users only
• Enable KASAN on development systems to detect similar memory safety issues

Patch Information

The vulnerability has been addressed in multiple kernel commits that defer hook memory release until RCU readers are done. Patches are available in the stable kernel trees:

• Kernel Git Commit 24f90fa3994b
• Kernel Git Commit 54244d54a971
• Kernel Git Commit c25e0dec366a
• Kernel Git Commit cb2bf5efdb02
• Kernel Git Commit d016c216bc75

The fix modifies the hook memory lifecycle to use call_rcu() or equivalent mechanisms to defer freeing until all RCU read-side critical sections have completed.

Workarounds

• Restrict access to netlink sockets capable of interacting with netfilter hooks using appropriate access controls
• Implement kernel module loading restrictions if netfilter BPF functionality is not required
• Use security frameworks like SELinux or AppArmor to limit which processes can interact with netfilter subsystem
• Consider disabling nfnetlink_hooks functionality if not required for your deployment