CVE-2026-68155

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

libceph: Reject monmaps advertising zero monitors

A message of type CEPH_MSG_MON_MAP contains a monmap that is sent from a

monitor to the client. This monmap contains information about the

existing monitors in the cluster. Currently, a monmap indicating that

there are zero monitors in the cluster is treated as valid. However, it

is impossible to have zero monitors in the cluster and still receive a

valid monmap from a monitor. Therefore, such a monmap must be corrupted

and should be treated as invalid. Furthermore, a monmap with a monitor

count of zero can subsequently crash the client when attempting to open

a session with a monitor in __open_session(). This happens because the

"BUG_ON(monc->monmap->num_mon < 1)" assertion in pick_new_mon() is

triggered.

This patch extends a check in ceph_monmap_decode() to also reject

arriving mon_maps with num_mon == 0 rather than only with

num_mon > CEPH_MAX_MON.

[ idryomov: dr

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References