CVE-2026-89656
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel, the libceph module has a vulnerability due to failure to reject buckets with mismatched CRUSH ids. The crush_decode() function stores data by array slot, and a malformed map can cause one bucket to reuse another bucket's workspace, leading to an out-of-bounds write. KASAN reports an out-of-bounds write in bucket_perm_choose().
Risk Assessment
A malicious or compromised Ceph monitor can supply a crafted CRUSH map causing an out-of-bounds memory write and potential code execution in kernel context. This affects confidentiality, integrity, and availability of Ceph clients.
Recommendation
Update the Linux kernel to a version with the fix that rejects buckets whose encoded id does not match their array slot. Limit trust in Ceph monitors within the cluster.
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Original NVD description (English source)
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.