CVE-2023-1206

What it actually does

Hash collision in the Linux kernel IPv6 connection lookup table allows crafted SYN packets to trigger excessive CPU consumption during table lookups, reaching up to 95% utilization.

Why it matters to the business

IPv6-enabled Linux servers can experience severe performance degradation or denial of service from attackers on the local network or with high-bandwidth access, potentially disrupting services and increasing operational costs.

How an attack unfolds

An attacker positioned on the local network or with sufficient bandwidth sends a stream of specially crafted IPv6 SYN packets that collide in the kernel's connection lookup hash table, forcing repeated expensive lookups and driving CPU usage to 95%.

How to fix it

Update the Linux kernel to a version containing commit 2dde18cd1d8fac735875f2e4987f11817cc0bc2c or later; rebuild and deploy the fixed kernel across all affected systems.

How to confirm the fix worked

Confirm the running kernel includes commit 2dde18cd1d8fac735875f2e4987f11817cc0bc2c via git log or version string checks; monitor CPU utilization under simulated IPv6 SYN traffic to verify mitigation.

Typical attack path

1. Locate Linux servers accepting IPv6 connections within local network range or reachable via high-bandwidth path
2. Craft IPv6 SYN packets engineered to produce hash collisions in the connection lookup table
3. Transmit sustained flood of colliding packets to the target
4. Observe CPU exhaustion on the server accepting the IPv6 connections

How to detect it

Review system logs and performance metrics for sudden sustained CPU spikes correlated with IPv6 SYN traffic; inspect network captures for unusual volumes of IPv6 SYN packets targeting the same destination.

What your security team should do

• Apply the kernel patch containing commit 2dde18cd1d8fac735875f2e4987f11817cc0bc2c as the highest priority
• Restrict IPv6 exposure to trusted networks where feasible until patched
• Monitor for anomalous IPv6 traffic volumes and corresponding CPU spikes
• Test patched kernels in staging before broad deployment