CVE-2026-98011 net/sched: hhf: clamp quantum in change and init paths
A local attacker with CAP_NET_ADMIN can cause a kernel soft lockup and denial of service by setting a low quantum value in the HHF qdisc.
- 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-2026-98011?
CVE-2026-98011 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: hhf: clamp quantum in change and init paths
hhf_change() accepts any quantum from userspace, including 1. With a crafted size table qdisc_pkt_len reaches ~2 GiB, so quantum=1 makes the deficit-refill loop spin ~2^31 times under the qdisc lock (a soft lockup / denial of service).
Add max(256U, ...) in hhf_change() matching fq_codel_change(). Clamp hhf_init() to [256, 1<<20] matching the siblings, and remove the old fallback that only set quantum=256 on overflow.
Conditions to recreate the bug: CONFIG_NET_SCH_HHF=y. Requires CAP_NET_ADMIN (namespace-local via unshare -Urn suffices).
tc qdisc add dev dummy0 root hhf tc qdisc change dev dummy0 root hhf quantum 1 stab data 32768 size_log 15 cell_log 0
Which versions are affected by CVE-2026-98011?
How do I fix CVE-2026-98011?
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-2026-98011 being exploited?
There is no known exploitation of CVE-2026-98011 in the wild and no public exploit code.
Sources
Also known as AZL-104574, BELL-CVE-2026-98011, DEBIAN-CVE-2026-98011, GHSA-93pc-w6vh-hg9r, UBUNTU-CVE-2026-98011.