CVE-2026-97991 vdpa_sim_blk: reject out-of-range sector starts
A guest VM can trigger out-of-bounds reads and writes in the Linux kernel's vdpa_sim_blk driver, potentially leading to code execution or data exposure.
- 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-2026-97991?
CVE-2026-97991 is a high-severity memory corruption vulnerability in Linux, published on 25 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:
vdpa_sim_blk: reject out-of-range sector starts
vdpasim_blk_check_range() logs an invalid start sector but continues validating the request. The subsequent unsigned capacity subtraction can underflow and let an out-of-range buffer offset reach the data path.
The invalid offset is used by three request paths. VIRTIO_BLK_T_OUT copies guest data to blk->buffer + offset through vringh_iov_pull_iotlb(), causing an out-of-bounds write in _copy_from_iter() or memcpy(). VIRTIO_BLK_T_IN copies from blk->buffer + offset to the guest through vringh_iov_push_iotlb(), causing an out-of-bounds read in _copy_to_iter(). VIRTIO_BLK_T_WRITE_ZEROES passes blk->buffer + offset to memset(), causing an out-of-bounds write.
Reject starts at or beyond the capacity before the subtraction. Treat the capacity boundary as invalid because the IN and OUT paths round byte counts down to sectors for validation but later copy the original byte counts. A sub-sector request at the capacity boundary would otherwise still access past the end of the buffer.
I found this bug myself, though the patch was written with AI assistance.
Which versions are affected by CVE-2026-97991?
How do I fix CVE-2026-97991?
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-2026-97991 being exploited?
There is no known exploitation of CVE-2026-97991 in the wild and no public exploit code.
Sources
Also known as AZL-104381, BELL-CVE-2026-97991, DEBIAN-CVE-2026-97991, GHSA-hprw-93rc-4v5g, UBUNTU-CVE-2026-97991.