CVE-2026-23392: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-23392 is a use-after-free vulnerability in the Linux kernel's netfilter nf_tables subsystem, specifically in the flowtable error handling code path. The flaw occurs when the kernel fails to call synchronize_rcu() after unregistering hooks during error conditions, leaving the flowtable exposed to both the packet processing path and the nfnetlink_hook control plane after the memory has been freed. It affects Linux kernel versions from 4.16 through multiple stable series up to (but not including) 6.1.167, 6.6.130, 6.12.78, 6.18.20, and 6.19.10, as well as Microsoft Azure Linux 3 (azl3_kernel_6.6.126.1-1). The vulnerability was published on March 25, 2026, and carries a CVSS v3.1 base score of 7.8 (High) (Red Hat CVE, Feedly).

The root cause is classified as CWE-416 (Use After Free) and CWE-825 (Expired Pointer Dereference). When the nf_tables flowtable registration fails — typically due to reaching the maximum number of hooks or a hardware offload setup failure — the kernel unregisters the hooks but does not wait for an RCU grace period via synchronize_rcu() before freeing the flowtable structure. This race condition allows a concurrently executing hook or the nfnetlink_hook control plane (e.g., during a hook dump operation) to dereference the already-freed flowtable memory. The bug was uncovered by KASAN, which reported the use-after-free from the nfnetlink_hook path when dumping hooks. Exploitation requires local access with low privileges (e.g., the ability to interact with netfilter configuration) (Red Hat CVE, Kernel Announce).

Successful exploitation by an unprivileged local attacker can result in kernel memory corruption, potentially leading to a denial of service via kernel crash or, in more severe scenarios, privilege escalation to root. All three security dimensions are affected: confidentiality, integrity, and availability are each rated High in the CVSS assessment. The vulnerability is confined to the local system (no network-based exploitation), but privilege escalation could enable lateral movement within a compromised environment or full system takeover (Red Hat CVE, Feedly).

• Logs: Kernel logs (dmesg / /var/log/kern.log) showing KASAN use-after-free reports referencing nf_tables, nfnetlink_hook, or flowtable-related functions; unexpected kernel oops or BUG messages in the netfilter subsystem.
• Process/Behavior: Unexpected kernel panics or system reboots on hosts running netfilter/nftables with flowtable configurations; anomalous behavior when dumping netfilter hooks via nft or nfnetlink.
• System: Presence of unprivileged users with access to netfilter configuration (e.g., via user namespaces) on affected kernel versions; systems running kernel versions in the affected ranges (4.16–6.1.166, 6.2–6.6.129, 6.7–6.12.77, 6.13–6.18.19, 6.19–6.19.9) without applied patches.

Apply kernel updates to a patched version for your respective stable series: 6.1.167 or later, 6.6.130 or later, 6.12.78 or later, 6.18.20 or later, or 6.19.10 or later. Microsoft has released a patch for Azure Linux 3 (azl3_kernel_6.6.126.1-1). Red Hat has issued errata RHSA-2026:21556, RHSA-2026:21557, and RHSA-2026:23224; SUSE has released SUSE-SU-202621834-1 and SUSE-SU-20262217-1; Amazon Linux 2023 advisories ALAS2023-2026-1594 and ALAS2023-2026-1681 are also available. As a workaround, restrict unprivileged user access to netfilter configuration (e.g., by disabling unprivileged user namespaces where feasible) to reduce the attack surface (Red Hat Errata, SUSE Advisory, Amazon Linux).

The vulnerability was announced via the official Linux kernel CVE mailing list and tracked by multiple distribution vendors including Red Hat, SUSE, Debian, and Amazon Linux, all of whom issued timely patches (Kernel Announce, Red Hat Errata). Debian accepted the fix into unstable (linux 6.19.10-1) and stable-backports, and the Yocto Project security list also circulated advisories. No notable independent researcher commentary or significant social media discussion beyond routine CVE tracking has been observed for this vulnerability.