CVE-2026-89894 media: cx231xx: reject geometry changes while the VBI queue is busy
A local attacker can trigger a heap out-of-bounds write in the cx231xx VBI driver by changing video geometry while the VBI queue is active, potentially leading to code execution.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89894?
CVE-2026-89894 is a high-severity memory corruption vulnerability in Linux, published on 16 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:
media: cx231xx: reject geometry changes while the VBI queue is busy
vidioc_s_fmt_vid_cap() and vidioc_s_std() change the device-wide dev->width / dev->norm but only refuse the change when the *video* queue (dev->vidq) is busy. The VBI queue (dev->vbiq) shares that same geometry: cx231xx_init_vbi_isoc() latches dma_q->lines_per_field from dev->norm, the VBI videobuf2 plane is sized from dev->width / dev->norm in vbi_queue_setup() and vbi_buf_prepare(), and cx231xx_do_vbi_copy() then recomputes the destination offset from the *live* dev->width and the latched lines_per_field on every URB completion:
offset = lines_completed * (dev->width << 1) + ...; if (dma_q->current_field == 2) offset += dev->width * 2 * dma_q->lines_per_field; memcpy(plane + offset, p_buffer, lencopy);
Because the VBI node shares video_ioctl_ops with the video node, an application can size a small VBI plane (REQBUFS/QBUF with a small width, or with the NTSC standard), then enlarge dev->width (or switch dev->norm to PAL) through the video node while the VBI stream is running -- the change is allowed because only dev->vidq is checked -- and let the device deliver a field-2 VBI payload. cx231xx_do_vbi_copy() now computes the offset with the larger geometry and memcpy()s past the end of the smaller plane that was already allocated, a heap out-of-bounds write whose offset is attacker-chosen and whose contents come from the device. The per-field guard in cx231xx_copy_vbi_line() does not help: it bounds the copy against the latched lines_per_field, not the plane's real capacity, and vb2 does not re-run buf_prepare() for an already prepared buffer.
Refuse the format/standard change when the VBI queue is busy as well, so the geometry cannot change underneath an allocated VBI buffer.
Which versions are affected by CVE-2026-89894?
How do I fix CVE-2026-89894?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-89894 being exploited?
There is no known exploitation of CVE-2026-89894 in the wild and no public exploit code.
Sources
Also known as AZL-101478, BELL-CVE-2026-89894, DEBIAN-CVE-2026-89894, GHSA-c3cf-vcgj-vrgp, UBUNTU-CVE-2026-89894.