CVE-2026-89653 ceph: reject export_targets ranks >= CEPH_MAX_MDS in mdsmap decode
A buffer overflow in the Linux kernel Ceph MDS map decoder allows attackers to write past array bounds, potentially causing crashes or code execution.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89653?
CVE-2026-89653 is a critical memory corruption vulnerability in Linux, published on 11 Sep 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:
ceph: reject export_targets ranks >= CEPH_MAX_MDS in mdsmap decode
MDSMap export_targets entries are monitor controlled. check_new_map() uses each entry as a bit number in a fixed stack bitmap, so a rank outside the protocol namespace can make set_bit() write past the end of the array.
Reject ranks outside CEPH_MAX_MDS while decoding the map. Do not validate against possible_max_rank here because maps may legitimately reference ranks beyond a temporarily reduced max_mds.
Which versions are affected by CVE-2026-89653?
How do I fix CVE-2026-89653?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-89653 being exploited?
There is no known exploitation of CVE-2026-89653 in the wild and no public exploit code.
Sources
Also known as AZL-100418, BELL-CVE-2026-89653, DEBIAN-CVE-2026-89653, GHSA-q4wh-f6ch-5m9w, UBUNTU-CVE-2026-89653.