CVE-2026-90072 net/sched: sfq: clamp quantum to avoid signed overflow soft lockup
A local attacker with CAP_NET_ADMIN can cause a kernel soft lockup by configuring a network device with an excessively large MTU, leading to a denial of service.
- 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-2026-90072?
CVE-2026-90072 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: sfq: clamp quantum to avoid signed overflow soft lockup
sfq_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) (unsigned). A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000, so slot->allot = INT_MIN and INT_MIN + INT_MIN toggles between INT_MIN and 0 forever, spinning sfq_dequeue() under the qdisc lock.
Clamp the quantum to [256, 1 << 20] so the refill loop terminates. The lower bound also covers q->quantum == 0 (psched_mtu() returning 0), which spins sfq_dequeue() identically. sfq_change() already rejects a negative quantum, so only the init path was exposed.
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-2026-90072?
How do I fix CVE-2026-90072?
Apply the vendor's patch.
Is CVE-2026-90072 being exploited?
There is no known exploitation of CVE-2026-90072 in the wild and no public exploit code.
Sources
Also known as AZL-102920, BELL-CVE-2026-90072, DEBIAN-CVE-2026-90072, GHSA-783h-5cfx-mm7x, UBUNTU-CVE-2026-90072.