CVE-2026-98009 net/sched: ets: clamp quantum in parse and fallback paths

Q: Is CVE-2026-98009 being exploited?

There is no known exploitation of CVE-2026-98009 in the wild and no public exploit code.

Not scored Published 25 Sep 2026 Updated 19 Oct 2026

A local attacker with CAP_NET_ADMIN can cause a kernel denial of service by triggering an infinite loop in the ETS qdisc scheduler.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-98009?

CVE-2026-98009 is a denial of service vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: ets: clamp quantum in parse and fallback paths

ets_qdisc_change() falls back to psched_mtu() with no floor for bands without an explicit quantum. With a crafted size table qdisc_pkt_len reaches ~2 GiB, so a zero psched_mtu on a headerless device makes the deficit-refill loop spin under the qdisc lock.

Move the floor into ets_quantum_parse() so explicitly configured quanta are also clamped to [256, 1<<20], not just the fallback path.

Conditions to recreate the bug: CONFIG_NET_SCH_ETS=y. Requires CAP_NET_ADMIN (namespace-local via unshare -Urn suffices).

tc qdisc add dev dummy0 root ets bands 3 strict 2 quanta 1 1

Which versions are affected by CVE-2026-98009?

How do I fix CVE-2026-98009?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-98009 being exploited?