CVE-2026-89650: Linux Vulnerability (CVSS 9.1)

Description

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.

Metrics

CVSS 3.1

9.1/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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	>= d463a43d69f4af85887671d76182437775fd1631, < 0c4bcc3ba7291d383b82ce1c2fe324f69a42da2d; >= d463a43d69f4af85887671d76182437775fd1631, < 55a06b32438c222765138727d0a8164b103e8f0d; >= d463a43d69f4af85887671d76182437775fd1631, < eb3e1a1cb1634c76d59c5a9cb1a026fc69d40911; >= d463a43d69f4af85887671d76182437775fd1631, < 3bf7dba8dba9a05774b846affec61a3624ddba38; >= d463a43d69f4af85887671d76182437775fd1631, < 58c2d3e954c13694ef6e820a5e9456461bb9e7df; >= d463a43d69f4af85887671d76182437775fd1631, < 332c444f4dc6fa1e8b8637c9e82d29e97f768656; >= d463a43d69f4af85887671d76182437775fd1631, < a3eb169ee297aa99670ba927c659990bd1e453f3
Linux	Linux	4.7

References

Timeline

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

Frequently Asked Questions

What is CVE-2026-89650?

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.

How severe is CVE-2026-89650?

CVE-2026-89650 has a CVSS score of 9.1/10 (CRITICAL severity). The EPSS model estimates a 0.46% probability of exploitation in the next 30 days.

How do I fix CVE-2026-89650?

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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