# CVE-2026-90090: Bluetooth: btmtksdio: Fix out-of-bounds DMA read in the TX path

> A local attacker with Bluetooth access can read uninitialized kernel memory via an out-of-bounds DMA read in the MediaTek SDIO Bluetooth driver.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102075, BELL-CVE-2026-90090, DEBIAN-CVE-2026-90090, GHSA-v2q7-g7pp-vm78, UBUNTU-CVE-2026-90090

## What is CVE-2026-90090?

CVE-2026-90090 is a vulnerability in Linux, published on 17 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:

Bluetooth: btmtksdio: Fix out-of-bounds DMA read in the TX path

btmtksdio_tx_packet() rounds the transfer size up to the SDIO block size
of 256 bytes, but hands the host controller the SKB buffer as is:

	err = sdio_writesb(bdev->func, MTK_REG_CTDR, skb->data,
			   round_up(skb->len, MTK_SDIO_BLOCK_SIZE));

Only skb->len bytes hold packet data, so the controller reads up to 255
bytes of uninitialised memory and sends it to the device over the SDIO
bus. Depending on how much tailroom slack the SKB allocation happens to
carry, that read can also extend past the end of the buffer.

Compute the padded length up front, ensure the SKB has tailroom for it,
and zero-fill the padding with skb_put_zero(). skb->len then covers the
padding, so sdio_writesb() no longer needs to round up. byte_tx keeps
counting the header and the payload only, and the error path restores the
SKB so that the caller can requeue it.

Writing behind skb->tail is only safe because the driver owns the buffer,
which "Bluetooth: btmtksdio: Take exclusive ownership of the SKB before
TX" ensures.

## Which versions are affected by CVE-2026-90090?


## How do I fix CVE-2026-90090?

Apply the vendor's patch.

## Is CVE-2026-90090 being exploited?

There is no known exploitation of CVE-2026-90090 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90090 and fix it if it is affected.

What it is: CVE-2026-90090 is a vulnerability in Linux, published on 17 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-2026-90090 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-2026-90090/ (Markdown: https://insights.sbomify.com/CVE-2026-90090/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90090
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90090
- OSV: https://osv.dev/vulnerability/CVE-2026-90090

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90090/
Summaries are generated and may contain mistakes; the official description above is the record.