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

Not scored Published 17 Sep 2026 Updated 19 Oct 2026

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

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

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.

Sources

Also known as AZL-102075, BELL-CVE-2026-90090, DEBIAN-CVE-2026-90090, GHSA-v2q7-g7pp-vm78, UBUNTU-CVE-2026-90090.