# CVE-2026-89973: nvme-tcp: check the data direction of a C2HData PDU

> A malicious NVMe controller can trigger a kernel warning by sending unexpected data, causing a denial of service on hosts configured to panic on warnings.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101208, BELL-CVE-2026-89973, DEBIAN-CVE-2026-89973, GHSA-9393-xpw8-3983, UBUNTU-CVE-2026-89973

## What is CVE-2026-89973?

CVE-2026-89973 is a high-severity denial of service vulnerability in Linux, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

nvme-tcp: check the data direction of a C2HData PDU

nvme_tcp_handle_c2h_data() finds the request by command id and checks
that it has a payload, but it does not check that the command asked for
data to be read.  A controller that answers a write command with C2HData
therefore reaches nvme_tcp_recv_data(), where _copy_to_iter() hits
WARN_ON_ONCE(i->data_source) and returns 0.  The receive path turns that
into -EFAULT and resets the controller.

No data is copied, so this is not memory corruption.  What a controller
gets is a kernel warning it can raise at will, which is fatal on a host
booted with panic_on_warn.

The send path already knows the direction - it consults rq_data_dir()
when it builds a command - and nvme_tcp_handle_r2t() checks the length
and the offset of the request it names.  The C2HData path does not check
the direction at all.

Reject a C2HData PDU whose command is not a read.  Rejecting it fails
the command and resets the controller, as the neighbouring check in this
function does; what goes away is the warning.

  [    6.885580] ------------[ cut here ]------------
  [    6.886457] WARNING: lib/iov_iter.c:193 at _copy_to_iter+0x289/0x1330, CPU#0: kworker/0:1H/71
  [    6.888137] CPU: 0 UID: 0 PID: 71 Comm: kworker/0:1H Not tainted 7.2.0-rc5-NVMETCP-gf5098b6bae76 #1 PREEMPT(lazy)
  [    6.891165] Workqueue: nvme_tcp_wq nvme_tcp_io_work
  [    6.891875] RIP: 0010:_copy_to_iter+0x289/0x1330
  [    6.903739] Call Trace:
  [    6.904085]  <TASK>
  [    6.909254]  __skb_datagram_iter+0x433/0x820
  [    6.911026]  skb_copy_datagram_iter+0x37/0x120
  [    6.911622]  nvme_tcp_recv_skb+0xa07/0x4320
  [    6.913378]  __tcp_read_sock+0x1ab/0x810
  [    6.915788]  nvme_tcp_try_recv+0x152/0x1e0
  [    6.918222]  nvme_tcp_io_work+0x1e4/0x6c0
  [    6.926906]  </TASK>
  [    6.927226] ---[ end trace 0000000000000000 ]---
  [    6.927878] nvme nvme0: queue 1 failed to copy request 0x71 data
  [    6.928709] nvme nvme0: receive failed:  -14

## Which versions are affected by CVE-2026-89973?


## How do I fix CVE-2026-89973?

Apply the vendor's patch.

## Is CVE-2026-89973 being exploited?

There is no known exploitation of CVE-2026-89973 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89973 and fix it if it is affected.

What it is: CVE-2026-89973 is a high-severity denial of service vulnerability in Linux, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89973 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-2026-89973/ (Markdown: https://insights.sbomify.com/CVE-2026-89973/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89973
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89973
- OSV: https://osv.dev/vulnerability/CVE-2026-89973

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89973/
Summaries are generated and may contain mistakes; the official description above is the record.