# CVE-2026-89968: nvmet-tcp: reject unsolicited H2CData PDUs

> Remote attackers can cause a kernel soft-lockup in the NVMe/TCP target by sending unsolicited data PDUs, requiring an allow_any_host configuration.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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-101328, BELL-CVE-2026-89968, DEBIAN-CVE-2026-89968, GHSA-46h3-r5w2-2vqq, UBUNTU-CVE-2026-89968

## What is CVE-2026-89968?

CVE-2026-89968 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:

nvmet-tcp: reject unsolicited H2CData PDUs

nvmet_tcp_handle_h2c_data_pdu() accepts an H2CData PDU after only checking
that its TTAG is a valid in-range command index and that the command's
data buffers are mapped. It never checks that the target has actually
solicited that data by sending an R2T for the command.

A remote host can abuse this. It submits a write command that takes the
R2T path and, before the target transmits the R2T, sends an H2CData PDU
for that command's tag. The data completes the command early, and when
the command then fails synchronously (e.g. a length mismatch caught by
nvmet_check_transfer_len()), it is completed a second time. Each
completion calls nvmet_tcp_queue_response(), so the same command is added
to queue->resp_list twice while it is still linked; the second llist_add()
makes the node point to itself (lentry->next == lentry).

nvmet_tcp_process_resp_list() then walks that self-referential node and
adds the command to resp_send_list twice. With CONFIG_DEBUG_LIST this
trips the "list_add double add" check (kernel BUG); without it the loop
never terminates and the nvmet_tcp workqueue wedges (soft-lockup). It is
remotely triggerable and needs no authentication on an allow_any_host
subsystem.

Track whether an R2T has been transmitted for a command and reject an
H2CData PDU that arrives before it. The flag is cleared on command reuse
(nvmet_tcp_get_cmd() zeroes cmd->flags) and stays set across the multiple
H2CData PDUs of a single solicited transfer.

## Which versions are affected by CVE-2026-89968?


## How do I fix CVE-2026-89968?

Apply the vendor's patch.

## Is CVE-2026-89968 being exploited?

There is no known exploitation of CVE-2026-89968 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89968 and fix it if it is affected.

What it is: CVE-2026-89968 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-2026-89968 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-2026-89968/ (Markdown: https://insights.sbomify.com/CVE-2026-89968/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89968
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89968
- OSV: https://osv.dev/vulnerability/CVE-2026-89968

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89968/
Summaries are generated and may contain mistakes; the official description above is the record.