CVE-2026-90073 net/sched: hhf: clamp quantum before hhf_change() to avoid overflow
A local attacker with CAP_NET_ADMIN can cause a kernel denial of service via integer overflow in the HHF qdisc when using devices with huge MTUs.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90073?
CVE-2026-90073 is a vulnerability in Linux, published on 17 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 before hhf_change() to avoid overflow
hhf_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) with no overflow check. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes weight * quantum overflow the signed deficit in hhf_dequeue(), spinning forever.
Clamp q->quantum before hhf_change() so both the opt and !opt paths see a sane quantum. Without this, bare "tc qdisc add ... hhf" succeeds with a clamped quantum but "tc qdisc add ... hhf limit 1000" (any option present) fails with -EINVAL because hhf_change() re-validates the unclamped default (sch_hhf.c:559). 256 matches fq_codel's floor and is a sane minimum for a DRR quantum.
Conditions to recreate the bug: a device whose MTU (plus hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace.
Which versions are affected by CVE-2026-90073?
How do I fix CVE-2026-90073?
Apply the vendor's patch.
Is CVE-2026-90073 being exploited?
There is no known exploitation of CVE-2026-90073 in the wild and no public exploit code.
Sources
Also known as AZL-102557, BELL-CVE-2026-90073, DEBIAN-CVE-2026-90073, GHSA-xxq9-2g6r-mm98, UBUNTU-CVE-2026-90073.