# CVE-2026-89969: nvmet-tcp: fix out-of-bounds write when receiving an over-long PDU

> A remote unauthenticated attacker can trigger an out-of-bounds write in the Linux kernel's nvmet-tcp module by sending a crafted PDU, potentially leading to memory corruption and code execution.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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-101600, BELL-CVE-2026-89969, DEBIAN-CVE-2026-89969, GHSA-pcvm-4g32-rvg7, UBUNTU-CVE-2026-89969

## What is CVE-2026-89969?

CVE-2026-89969 is a critical memory corruption 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: fix out-of-bounds write when receiving an over-long PDU

nvmet_tcp_try_recv_pdu() reads a PDU header into the fixed 128-byte
queue->pdu union, then computes the remaining payload length as

	queue->left = hdr->hlen - queue->offset + hdgst;

and reads that many more bytes into &queue->pdu + queue->offset, without
ever bounding the result against sizeof(queue->pdu).

A struct nvme_tcp_icreq_pdu is itself 128 bytes, exactly the size of the
union. Once a header digest has been negotiated (hdgst = 4), a second
ICReq passes the hlen == nvmet_tcp_pdu_size() check but yields
queue->left = 128 - 8 + 4 = 124, so bytes 8..132 are written into the
128-byte buffer -- 4 bytes past its end, over queue->hdr_digest and
queue->data_digest. Those bytes are attacker-controlled (an ICReq
carries no digest), and the duplicate ICReq is only rejected later,
after the overflow. A remote unauthenticated host can thus corrupt
kernel memory adjacent to the receive buffer.

Reject any PDU whose declared length would read past the end of
queue->pdu before the second recv.

## Which versions are affected by CVE-2026-89969?


## How do I fix CVE-2026-89969?

Apply the vendor's patch.

## Is CVE-2026-89969 being exploited?

There is no known exploitation of CVE-2026-89969 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89969 and fix it if it is affected.

What it is: CVE-2026-89969 is a critical memory corruption 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-2026-89969 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-2026-89969/ (Markdown: https://insights.sbomify.com/CVE-2026-89969/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89969
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89969
- OSV: https://osv.dev/vulnerability/CVE-2026-89969

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89969/
Summaries are generated and may contain mistakes; the official description above is the record.