CVE-2026-89650
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel, ceph_mdsmap_decode() lacked bounds checking for the num_export_targets array in MDS info records with version 2 or 3. A malicious or compromised Ceph monitor can send an MDS map with an oversized num_export_targets value, causing an out-of-bounds read in the CephFS client kernel.
Risk Assessment
The vulnerability allows an attacker controlling a Ceph monitor, or an on-path attacker on an unsigned/unencrypted session, to trigger an out-of-bounds read in the client kernel, potentially causing a kernel panic. No information leak to the attacker was reported.
Recommendation
Update the Linux kernel to a version containing the fix that adds a ceph_decode_need() check for the export-targets array before advancing the cursor. Until patched, consider securing Ceph monitor sessions by enabling signing and encryption.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: ceph: bound num_export_targets array for mds info v2/v3 ceph_mdsmap_decode() in fs/ceph/mdsmap.c reads num_export_targets from each per-mds info record and advances the decode cursor by num_export_targets * sizeof(u32) without first checking that many bytes remain. The only upper-bound check that catches a runaway cursor (*p > info_end) is gated on info_v >= 4, because info_end is left NULL for info_v 2 and 3. When the monitor sends an MDS map whose per-mds info version is 2 or 3 with an oversized num_export_targets, the cursor moves past the message front buffer and the later export-targets loop calls the unchecked ceph_decode_32() on out-of-bounds memory. A kernel client processes CEPH_MSG_MDS_MAP from its monitor session (net/ceph/mon_client.c dispatches it; fs/ceph/super.c routes it to ceph_mdsc_handle_mdsmap(), which sets end to the front buffer bound and calls ceph_mdsmap_decode()). A malicious or compromised monitor, or an on-path attacker on an unsigned/unencrypted messenger session, can therefore drive an out-of-bounds read in the client kernel; on x86_64 with KASAN it is reported as a slab-out-of-bounds read in ceph_mdsmap_decode(). The decoded values land in the internal info->export_targets[] array, so the consequence is a kernel out-of-bounds read, not an information leak to the attacker. Impact: a malicious or compromised Ceph monitor sending an MDS map with a per-mds info version of 2 or 3 and an oversized num_export_targets field triggers an out-of-bounds read in the CephFS client kernel. Add a ceph_decode_need() for the export-targets array before advancing the cursor, so the bound is enforced for every info_v >= 2, not only info_v >= 4. This mirrors the count-then-need idiom already used for m_data_pg_pools later in the same function. Compute the export-targets byte count with size_mul() and reuse that checked length when advancing the cursor, so the attacker-controlled num_export_targets multiplication fails closed on overflow rather than relying on the later kcalloc() guard.