# CVE-2026-98022: net: cap tx_queue_len at S16_MAX to prevent oversized ring allocations

> An unprivileged user can exhaust system memory by setting an oversized tx_queue_len, causing a denial of service in the Linux kernel.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-104417, BELL-CVE-2026-98022, DEBIAN-CVE-2026-98022, GHSA-vfx5-qp78-q7gw, UBUNTU-CVE-2026-98022

## What is CVE-2026-98022?

CVE-2026-98022 is a denial of service vulnerability in Linux, published on 25 Sep 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: cap tx_queue_len at S16_MAX to prevent oversized ring allocations

Several subsystems allocate ring buffers sized by dev->tx_queue_len
with no upper bound. An unprivileged user (via unshare -Urn) can set a
huge tx_queue_len and exhaust global memory with ring allocations:

- pfifo_fast: pfifo_fast_init() and pfifo_fast_change_tx_queue_len()
  allocate 3 skb_array rings of tx_queue_len entries each.
- tun: tun_queue_resize() and the queue-attach path resize ptr_rings
  to tx_queue_len on the NETDEV_CHANGE_TX_QUEUE_LEN notifier.
- tap (macvtap/ipvtap): tap_queue_resize() and tap_init() resize/init
  ptr_rings to tx_queue_len on the same notifier.

netif_change_tx_queue_len() is the single entry point for IFLA_TXQLEN,
sysfs, and the SIOCSIFTXQLEN ioctl. Cap new_len at S16_MAX (32767)
there so the oversized value is rejected at set time. This takes
effect whether the device is up or down, before dev->tx_queue_len is
written, before any notifier fires, and before any ring is allocated.
The "> S16_MAX" check also subsumes the previous unsigned-long
truncation test, and a negative ifr_qlen from the ioctl lands far
above the cap after conversion, so both old failure modes are covered
by the one comparison.

tx_queue_len is ambigious: both a per-ring sizing multiplier and a
default queue-length/limit knob for consumers that allocate
nothing at set time (pfifo/bfifo/gred/plug/sfb limits, htb
direct_qlen, qfq max_classes, teql). 32767 is chosen as the largest
value NLA_POLICY_FULL_RANGE can express for the u32 IFLA_TXQLEN
policy in patch 2/3 while staying a legitimate queue length on
high-BDP paths; the ring-memory trade-off of a shared knob is
disclosed below.

Conditions to recreate the bug:
- CONFIG_NET_SCHED=y, CONFIG_VETH=y, CONFIG_USER_NS=y, CONFIG_NET_NS=y.
- Unprivileged user in a fresh user+net namespace (unshare -Urn).
- pfifo_fast: create veth pairs, set tx_queue_len to 500000, attach
  mq+pfifo_fast. ~28 iterations OOMs a 2GB guest.
- tun: create 50 tun devices with IFF_MULTI_QUEUE, set tx_queue_len to
  500000, open 8 queues each. ~1.6GB of ptr_ring allocations OOMs a
  512MB guest.
- tap: same as tun with IFF_TAP. ~960MB OOMs a 512MB guest.
- On the fixed kernel the oversized tx_queue_len is rejected with
  -ERANGE at set time (all four paths: RTM_SETLINK, RTM_NEWLINK
  create, sysfs, ioctl - the latter two via this check, the former
  two via this check and the 2/3 parse policy respectively).

## Which versions are affected by CVE-2026-98022?


## How do I fix CVE-2026-98022?

Apply the vendor's patch.

## Is CVE-2026-98022 being exploited?

There is no known exploitation of CVE-2026-98022 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98022 and fix it if it is affected.

What it is: CVE-2026-98022 is a denial of service vulnerability in Linux, published on 25 Sep 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-2026-98022 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-2026-98022/ (Markdown: https://insights.sbomify.com/CVE-2026-98022/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98022
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98022
- OSV: https://osv.dev/vulnerability/CVE-2026-98022

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98022/
Summaries are generated and may contain mistakes; the official description above is the record.