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CVE-2026-89656
libceph: reject buckets with mismatched CRUSH ids
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem net/ceph. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89656 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
crush_decode() stores bucket data by array slot, and the mapper later derives the per-bucket workspace index from the decoded bucket id. A malformed map can therefore make one bucket reuse another bucket's workspace by encoding an id different from -1 - slot. For uniform buckets, the second replica selection expands the source bucket's permutation into that aliased workspace buffer. If the source bucket is larger than the aliased bucket, the write runs past the smaller permutation array and can escape the kvmalloc'd CRUSH workspace. KASAN reports a slab OOB write of 4 bytes in bucket_perm_choose(). Reject buckets whose encoded id does not match their array slot. Valid CRUSH maps already use the canonical negative id corresponding to the bucket slot, so this restores the invariant expected by work->work[-1 - in->id] without changing valid map behavior.
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.
net/ceph/osdmap.c
- What this is
- CEPH COMMON CODE (LIBCEPH)MAINTAINERS section matched on net/ceph/ · ceph-devel@vger.kernel.org · Supported
- Kernel module
- libceph
Check it on the machine
grep -w CONFIG_CEPH_LIB /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 libcephPrints 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_LIB
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
- 0.51%, higher than 42.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/ceph
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.11 | 5.10.270 | ee59040d6ed1 |
| 4.11 | 5.15.221 | baad5875fdd2 |
| 4.11 | 6.1.188 | 4aeb93daadf3 |
| 4.11 | 6.6.157 | 6e5c6ce252b1 |
| 4.11 | 6.12.109 | 3516a4131c4e |
| 4.11 | 6.18.50 | 00562ccd4e88 |
| 4.11 | 7.2.4 | 79900d978158 |
| 4.11 | 7.3 | 3cde4a830230 |
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
- Malformed CRUSH data arrives in CEPH_MSG_OSD_MAP over TCP from a Ceph monitor (mon_dispatch) or OSD (osd_dispatch); crush_decode() stores attacker-chosen bucket ids and crush_do_rule() later indexes the workspace from those ids with no local syscall.
- AC:LAttack complexity, low
- A malicious monitor/OSD fully controls the OSD map and can encode a uniform bucket whose id aliases a smaller bucket's permutation buffer; the second replica expansion in bucket_perm_choose() then deterministically writes past the kvmalloc'd CRUSH workspace without races or rare configs.
- PR:NPrivileges required, none
- The attacker acts as the remote Ceph cluster peer delivering a forged osdmap to an already-connected kernel CephFS/RBD client and needs no local account, capabilities, or user-namespace privileges on the victim host.
- UI:NUser interaction, none
- Once a kernel Ceph client session exists, osdmap updates are applied automatically and scan_requests/kick_requests call calc_target()/crush_do_rule() without any further mount, open, or other victim interaction at exploit time.
- S:UScope, unchanged
- The out-of-bounds write corrupts kernel heap on the host running the Ceph client (the CRUSH workspace and adjacent kvmalloc memory), remaining in that kernel security domain rather than crossing a VM, container sandbox, or IOMMU boundary.
- C:HConfidentiality impact, high
- Aliasing a large uniform bucket onto a smaller permutation array performs an attacker-sized slab out-of-bounds write into adjacent kernel heap, which can be leveraged as a memory-corruption primitive for arbitrary kernel reads and information disclosure.
- I:HIntegrity impact, high
- bucket_perm_choose() writes the source bucket's permutation past the aliased workspace into adjacent kvmalloc memory, giving a kernel heap out-of-bounds write that can be used for control-flow hijacking and arbitrary code execution.
- A:HAvailability impact, high
- The slab out-of-bounds write reported by KASAN in bucket_perm_choose() can fault on unmapped adjacent memory or corrupt heap metadata, triggering a kernel oops or panic and complete loss of availability on affected Ceph client hosts.