# CVE-2026-98234: net/sched: hhf: cap hh_flows_limit at change time

> A local attacker with CAP_NET_ADMIN can cause unbounded memory growth and denial of service by setting an excessive hh_flows_limit in the HHF qdisc.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-106107, BELL-CVE-2026-98234, DEBIAN-CVE-2026-98234, GHSA-qgx8-c46g-4vmq, UBUNTU-CVE-2026-98234

## What is CVE-2026-98234?

CVE-2026-98234 is a denial of service vulnerability in Linux, published on 6 Oct 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: 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.

## Which versions are affected by CVE-2026-98234?


## How do I fix CVE-2026-98234?

Apply the vendor's patch.

## Is CVE-2026-98234 being exploited?

There is no known exploitation of CVE-2026-98234 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98234 and fix it if it is affected.

What it is: CVE-2026-98234 is a denial of service vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98234 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98234/ (Markdown: https://insights.sbomify.com/CVE-2026-98234/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98234
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98234
- OSV: https://osv.dev/vulnerability/CVE-2026-98234

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98234/
Summaries are generated and may contain mistakes; the official description above is the record.