# CVE-2026-89650

## Summary

- **CVE ID:** CVE-2026-89650
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## 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.

## Affected Products

- Linux — Linux (d463a43d69f4af85887671d76182437775fd1631)
- Linux — Linux (4.7)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/3bf7dba8dba9a05774b846affec61a3624ddba38)
- [CNA](https://git.kernel.org/stable/c/58c2d3e954c13694ef6e820a5e9456461bb9e7df)
- [CNA](https://git.kernel.org/stable/c/332c444f4dc6fa1e8b8637c9e82d29e97f768656)
- [CNA](https://git.kernel.org/stable/c/a3eb169ee297aa99670ba927c659990bd1e453f3)
- [CNA](https://git.kernel.org/stable/c/0c4bcc3ba7291d383b82ce1c2fe324f69a42da2d)
- [CNA](https://git.kernel.org/stable/c/55a06b32438c222765138727d0a8164b103e8f0d)
- [CNA](https://git.kernel.org/stable/c/eb3e1a1cb1634c76d59c5a9cb1a026fc69d40911)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.51%
- **EPSS Percentile:** 42.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-19._