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CVE-2026-89653
ceph: reject export_targets ranks >= CEPH_MAX_MDS in mdsmap decode
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem fs/ceph. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89653 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/ceph/mdsmap.c
- What this is
- CEPH DISTRIBUTED FILE SYSTEM CLIENT (CEPH)MAINTAINERS section matched on fs/ceph/ · ceph-devel@vger.kernel.org · Supported
- Kernel module
- ceph
Check it on the machine
grep -w CONFIG_CEPH_FS /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w cephPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_CEPH_FS
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.50%, higher than 41.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/ceph
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.15 | 5.15.221 | 3740c88ca9cb |
| 5.15 | 6.1.188 | 8c823bbab3c2 |
| 5.15 | 6.6.157 | c4addccd05ba |
| 5.15 | 6.12.109 | 736adee11af3 |
| 5.15 | 6.18.50 | 4d298880f82c |
| 5.15 | 7.2.4 | 96c3f5fbb0d5 |
| 5.15 | 7.3 | aedc9053d909 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- A crafted MDSMap arrives in CEPH_MSG_MDS_MAP over the Ceph messenger TCP session from a monitor or MDS; extra_mon_dispatch() and mds_dispatch() deliver it to ceph_mdsc_handle_mdsmap() on already-mounted CephFS/Rook/Kubernetes clients without a local syscall.
- AC:LAttack complexity, low
- The monitor fully controls each export_targets[] u32; after the first map is stored, a later epoch reaches check_new_map() and set_bit() with an attacker-chosen bit number, overflowing the stack bitmap with no race or special layout.
- PR:NPrivileges required, none
- The attacker is the remote Ceph monitor or MDS peer and needs no Linux UID, capability, or init-namespace root on the victim, matching other Ceph client decode CVEs such as CVE-2026-68159.
- UI:NUser interaction, none
- Once CephFS is mounted, MDS maps are subscribed and applied automatically in the ceph-msgr worker; a malicious peer can push a new epoch without any further interactive victim action.
- S:UScope, unchanged
- The stack out-of-bounds write corrupts kernel memory on the Ceph client host only and does not cross a VM, IOMMU, or sandbox security authority.
- C:HConfidentiality impact, high
- set_bit() with an attacker-chosen rank writes past the fixed stack bitmap in check_new_map(), corrupting adjacent kernel stack contents; this memory-corruption primitive can be leveraged for information disclosure.
- I:HIntegrity impact, high
- The overflow is a stack out-of-bounds write of attacker-selected bits at a u32-controlled offset from the targets[] array, enabling control-flow hijack and arbitrary kernel writes.
- A:HAvailability impact, high
- An out-of-range bit index makes set_bit() write off the stack object, causing a KASAN stack-out-of-bounds report or kernel oops/panic that a malicious monitor can repeat with each new map epoch.