CVE-2023-52581

What it actually does

A u8 counter in nftables garbage collection wraps after 255 expired elements, causing reuse of the initial gc container instead of allocating a new one; this leaks memory for prior elements and leads to a use-after-free when the structure is dereferenced after being passed to call_rcu.

Why it matters to the business

Linux systems using nftables may suffer gradual memory exhaustion and instability when handling sets with frequent element expiration, increasing operational risk and potential downtime in network-heavy deployments.

How an attack unfolds

An attacker with privileges to manage nftables sets adds elements configured for expiration, forces more than 255 expirations to trigger the wraparound and leak, then leverages the resulting memory corruption or use-after-free to escalate privileges or crash the system.

How to fix it

Upgrade the Linux kernel to a version containing commit 7cf055b43756b10aa2b851c927c940f5ed652125 or later; rebuild and reboot with the fixed kernel.

How to confirm the fix worked

Verify the running kernel contains commit 7cf055b43756b10aa2b851c927c940f5ed652125; monitor nftables set operations and memory usage under load to confirm leak is resolved.

Typical attack path

1. Obtain CAP_NET_ADMIN or root access on the target host
2. Create or modify an nftables set with expiration timers
3. Add and expire more than 255 set elements to trigger the gc wraparound
4. Trigger memory leak accumulation followed by use-after-free dereference

How to detect it

Review kernel logs and dmesg for nftables gc or memory allocation anomalies; correlate high memory growth with nftables set activity on production systems.

What your security team should do

• Apply the fixed kernel version immediately on all affected systems
• Restrict nftables management to trusted processes only
• Monitor memory consumption on hosts using nftables sets with expiration