CVE-2026-89656: Linux Vulnerability (CVSS 9.8)

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.46%

38.8th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 66a0e2d579dbec5c676cfe446234ffebb267c564, < ee59040d6ed1a5f8d10d27174b8f32c90ca8e89a; >= 66a0e2d579dbec5c676cfe446234ffebb267c564, < baad5875fdd2f5e248250fc3519bb045d64f1716; >= 66a0e2d579dbec5c676cfe446234ffebb267c564, < 4aeb93daadf388e72073abc204312dd364eeb30a; >= 66a0e2d579dbec5c676cfe446234ffebb267c564, < 6e5c6ce252b1eccfd41670a5cf95ab44f7ba7022; >= 66a0e2d579dbec5c676cfe446234ffebb267c564, < 3516a4131c4e45d62ee4e42e82c36930e8c1fbbd; >= 66a0e2d579dbec5c676cfe446234ffebb267c564, < 00562ccd4e88d092b9b851df50fad20442bfeb24; >= 66a0e2d579dbec5c676cfe446234ffebb267c564, < 79900d978158b2d80eef952fc41b9e4dc58d7b83; >= 66a0e2d579dbec5c676cfe446234ffebb267c564, < 3cde4a8302301679937474a5f7a851394cc1bd11
Linux	Linux	4.11

References

Timeline

Published: Sep 11, 2026
Last Modified: Sep 14, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-89656?

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.

How severe is CVE-2026-89656?

CVE-2026-89656 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 0.46% probability of exploitation in the next 30 days.

How do I fix CVE-2026-89656?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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