CVE-2024-27015

What it actually does

Incorrect assumption about PPPoE header location at network header offset causes flowtable tuple mismatch, forcing PPPoE packets onto the classical forwarding path instead of the optimized flowtable entry.

Why it matters to the business

Systems handling PPPoE traffic experience degraded network forwarding performance and higher CPU usage on the classical path; the issue is local and availability-focused with no data exposure.

How an attack unfolds

An attacker sends crafted or normal PPPoE traffic to an ingress interface on a Linux system with netfilter flowtable enabled; the incorrect header offset prevents tuple matching so packets bypass the fast path and consume additional resources, amplifying load.

How to fix it

Upgrade the Linux kernel to a version containing commit e719b52d0c56989b0f3475a03a6d64f182c85b56 (or the equivalent 4bed3b34dcc01fe6661f39c0e5d2285b340f7cac) in the stable tree; rebuild and reboot affected systems.

How to confirm the fix worked

Confirm the running kernel contains the listed commit hash via git log or kernel version string; test PPPoE traffic to verify flowtable entries are now matched correctly at ingress.

Typical attack path

1. Attacker generates or forwards PPPoE frames toward the target interface
2. Kernel netfilter flowtable performs tuple lookup using the wrong header offset
3. Lookup fails to match existing entry due to PPPoE header misplacement
4. Packets fall back to classical forwarding path increasing CPU and latency
5. Sustained traffic volume leads to measurable availability impact

How to detect it

Review kernel logs and netfilter flowtable statistics for unexpected fallback to classical forwarding on PPPoE interfaces; correlate with increased CPU on network processing paths.

What your security team should do

• Apply the referenced kernel commit or later stable release immediately on any system using netfilter flowtable with PPPoE
• Prioritize patching for routers, gateways, or appliances that process PPPoE traffic
• Monitor EPSS and KEV status for any future change in exploit maturity