CVE-2023-3777

What it actually does

Use-after-free in nf_tables_delrule() allows a bound chain's owner rule to free objects while they remain referenced during table rule flushing, enabling memory corruption for local privilege escalation.

Why it matters to the business

Local attackers on affected Linux systems can obtain full root access, compromising the entire host and any workloads or data it protects; the vulnerability has been public for over three years with no observed widespread exploitation.

How an attack unfolds

An attacker with a local account crafts nf_tables operations that trigger nf_tables_delrule() on a bound chain, causing the owner rule to release objects that are later reused, resulting in arbitrary kernel code execution and privilege escalation to root.

How to fix it

Upgrade the Linux kernel to include commit 6eaf41e87a223ae6f8e7a28d6e78384ad7e407f8 or later; apply the fix via distribution kernel packages that contain this commit.

How to confirm the fix worked

Verify the running kernel contains commit 6eaf41e87a223ae6f8e7a28d6e78384ad7e407f8 or is built from a source tree after that commit; test that nf_tables_delrule() no longer permits the described object release on bound chains.

Typical attack path

1. Obtain local user access on a vulnerable Linux kernel
2. Load or interact with the nf_tables netfilter subsystem
3. Create a bound chain and associated rules
4. Invoke nf_tables_delrule() to flush rules under the specific un-checked conditions
5. Trigger reuse of freed objects to corrupt kernel memory
6. Execute payload to escalate to root privileges

How to detect it

Review kernel logs and audit records for unusual nf_tables operations or rule deletions on bound chains; look for crashes or memory corruption indicators in dmesg around netfilter activity.

What your security team should do

• Prioritize patching all Linux systems to a kernel containing the referenced commit within standard change windows
• Restrict untrusted local user access on systems that cannot be immediately updated
• Monitor for new kernel releases from distributions and apply updates promptly