CVE-2026-68155 libceph: Reject monmaps advertising zero monitors
A malicious monitor can send a zero-monitor map to crash the Linux kernel Ceph client, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-68155?
CVE-2026-68155 is a high-severity denial of service vulnerability in Linux, published on 10 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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: drop "log output for unusual values of num_mon" part ]
Weakness: CWE-20
Which versions are affected by CVE-2026-68155?
How do I fix CVE-2026-68155?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-68155 being exploited?
There is no known exploitation of CVE-2026-68155 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-68155, DEBIAN-CVE-2026-68155, GHSA-2v58-jx7r-h3cm, UBUNTU-CVE-2026-68155.