CVE-2026-80970 ALSA: FCP: do not copy out an uninitialised init response

What is CVE-2026-80970?

CVE-2026-80970 is a vulnerability in Linux, published on 11 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:

ALSA: FCP: do not copy out an uninitialised init response

fcp_ioctl_init() allocates its response buffer with kmalloc() and copies the whole buffer back to userspace:

buf_size = init.step0_resp_size + init.step2_resp_size;

void *resp __free(kfree) = kmalloc(buf_size, GFP_KERNEL); ... if (copy_to_user(arg->resp, resp, buf_size)) return -EFAULT;

Nothing clears the buffer, and the only writer of its leading step0_resp_size bytes is the step-0 control transfer:

err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), FCP_USB_REQ_STEP0, USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN, 0, private->bInterfaceNumber, step0_resp, private->step0_resp_size); if (err < 0) return err;

usb_fill_control_urb() does not set URB_SHORT_NOT_OK, so a short or zero-length data stage completes with status 0 and snd_usb_ctl_msg() returns a small actual_length. The only check is err < 0, so a short transfer is accepted as success.

snd_usb_ctl_msg() copies the full size back unconditionally:

buf = kmemdup(data, size, GFP_KERNEL); ... memcpy(data, buf, size);

Bytes the device never wrote are therefore restored into resp unchanged and copied to userspace. step0_resp_size and step2_resp_size are each validated only to 1..255, so the caller also picks the slab cache, from kmalloc-8 up to kmalloc-512.

On 7.2.0-rc5 (arm64), device answering step 0 with a zero-length data stage, s0 = s2 = 255:

# init_on_alloc off, no spray step0 window [0,255): nonzero=94/255 000: 00 80 60 06 00 00 ff ff 18 00 00 00 57 01 ea 01 010: 08 78 22 13 00 00 ff ff a8 c4 5f 80 00 80 ff ff

# same kernel, kmalloc-512 pre-seeded with an 8-byte tag step0 window [0,255): nonzero=219/255 tagbytes=232

# identical run, init_on_alloc=1 step0 window [0,255): nonzero=0/255 tagbytes=0

# all three runs step2 window [255,510): device words matched=62/62

a8 c4 5f 80 00 80 ff ff is the little-endian kernel text address ffff8000805fc4a8. The step-2 window is unaffected, so the disclosure is exactly the step-0 region.

Zero the buffer, and require the step-0 transfer to deliver the full step0_resp_size bytes so a short data stage is reported as an error.

Discovered by XBOW, triaged by Baul Lee <[email protected]>

Which versions are affected by CVE-2026-80970?

How do I fix CVE-2026-80970?

Apply the vendor's patch.

Is CVE-2026-80970 being exploited?

There is no known exploitation of CVE-2026-80970 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2026-80970, DEBIAN-CVE-2026-80970, GHSA-x4cq-72c3-qv9j, UBUNTU-CVE-2026-80970.