CVE-2026-98011: net/sched: hhf: clamp quantum in change and init paths

Severity: unknown
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-25 · updated 2026-10-19

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

Affected products

Linux kernel: 3.14 — fixed in 7.3

How to fix

Upgrade to a fixed version: Linux kernel 7.3. Check the vendor advisory for mitigations.

References

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