CVE-2026-89657

Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source

AV:NAttack vector, network

The malformed sparse-read extent map is consumed in osd_sparse_read() on the Ceph messenger TCP receive path (messenger_v1/v2) when a kernel CephFS client handles an MOSDOpReply from a remote OSD; no local syscall or ioctl is required to parse the reply.

AC:LAttack complexity, low

A malicious OSD fully controls the sparse extent offsets and lengths and can advertise a far-forward nonzero extent with a matching data length, deterministically advancing the message-data cursor past the request buffer into BUG_ON(!*length) in ceph_msg_data_next() with no race or special memory layout.

PR:NPrivileges required, none

The attacker acts as a remote Ceph OSD peer on a compromised or attacker-controlled cluster and needs no account, capabilities, or user-namespace privileges on the victim Linux host; any kernel CephFS client connected to that cluster is exposed.

UI:NUser interaction, none

Once CephFS is mounted with fscrypt-encrypted files or the sparseread option, netfs/buffered reads and encrypted RMW writes issue CEPH_OSD_OP_SPARSE_READ as normal I/O; the OSD can crash the client on the next such reply without further victim action at exploit time.

S:UScope, unchanged

The BUG_ON panic occurs in the kernel Ceph client's receive path on the same host and does not cross a VM, IOMMU, or sandbox boundary to another security authority.

C:NConfidentiality impact, none

ceph_msg_data_next() hits BUG_ON(!*length) and related cursor assertions when the buffer is exhausted, before any out-of-bounds page access; there is no use-after-free, OOB read, or other information-disclosure primitive.

I:NIntegrity impact, none

Cursor over-advance is stopped by BUG_ON assertions rather than writing past the allocated request pages; hole-zeroing via zero_user_segment stays inside the destination buffer until the panic, so there is no arbitrary kernel write or control-flow hijack.

A:HAvailability impact, high

BUG_ON(!*length) in ceph_msg_data_next() on the client receive path causes a kernel oops or panic, fully denying availability of the affected Ceph client host until reboot.