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CVE-2026-89990
ceph: lock mutex in ceph_mds_check_access()
Published 2026-09-16 (33 days ago) by the Linux kernel CNA. Subsystem fs/ceph. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-89990 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| 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
MDS session OPEN handling replaces mdsc->s_cap_auths under mdsc->mutex, freeing the previous array and its strings. ceph_mds_check_access() traverses this array without holding the mutex. A concurrent session reopen can therefore free the array while it is being inspected, resulting in a use-after-free like this: Unable to handle kernel paging request at virtual address 003aaad64b2c8bb9 [...] Internal error: Oops: 0000000096000004 [#1] SMP Modules linked in: CPU: 56 UID: 2953037534 PID: 1253231 Comm: php-cgi8.4 Not tainted 6.18.45-i2-ampere #1146 NONE [..] pc : ceph_mds_check_access+0xd4/0x550 lr : ceph_mds_check_access+0xc8/0x550 [...] Call trace: ceph_mds_check_access+0xd4/0x550 (P) ceph_atomic_open+0x138/0xbe8 path_openat+0xa24/0xfa8 do_filp_open+0x94/0x158 do_sys_openat2+0x88/0xf8
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/mds_client.c
fs/ceph/mds_client.h
- 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
- 2026-09-16 (33 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
- 0.61%, higher than 48.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.10 | 6.12.110 | 729c1ff670ec |
| 6.10 | 6.18.51 | ca5bfea2045e |
| 6.10 | 7.2.5 | df1a97d5313f |
| 6.10 | 7.3 | a61c6ae1dae2 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| 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
- handle_session() frees mdsc->s_cap_auths on CEPH_SESSION_OPEN delivered over the Ceph messenger TCP session (mds_dispatch, CEPH_MSG_CLIENT_SESSION). CephFS re-exported via nfsd/ksmbd also lets a remote client reach the unlocked walker through ceph_atomic_open.
- AC:LAttack complexity, low
- A malicious MDS may send CEPH_SESSION_OPEN even on an already-open session, freeing and replacing s_cap_auths under mdsc->mutex at will. Concurrent open/unlink/setattr, including nfsd/ksmbd on a CephFS export, walk that array without the mutex; the MDS can retry while those operations are in flight.
- PR:NPrivileges required, none
- The attacker is the remote MDS peer, or an NFS/SMB client of a CephFS re-export, and needs no Linux UID, capability, or init-namespace root on the victim host, matching other MDS-driven CephFS client CVEs such as CVE-2026-89651.
- UI:NUser interaction, none
- Once CephFS is mounted, as is standard in Rook, Kubernetes, and OpenStack, SESSION_OPEN and VFS/nfsd opens run without any further interactive victim action such as mounting media or opening a user-supplied file at exploit time.
- S:UScope, unchanged
- The use-after-free corrupts kernel heap on the CephFS client host and remains in that kernel's security authority; it is not a VM escape, IOMMU bypass, or sandbox boundary crossing.
- C:HConfidentiality impact, high
- ceph_mds_check_access() and ceph_mds_auth_match() dereference the freed s_cap_auths array and its match.path, gids, and fs_name strings; a use-after-free of those objects enables arbitrary kernel read via heap reuse and is High per kernel UAF guidance.
- I:HIntegrity impact, high
- The same UAF is heap-sprayable with attacker-controlled SESSION_OPEN allocations (cap_auths_num and string lengths), yielding write and control-flow primitives; kernel guidance scores use-after-free integrity as High.
- A:HAvailability impact, high
- The reported oops is a kernel paging fault in ceph_mds_check_access from ceph_atomic_open on the freed array; repeating SESSION_OPEN while the walker runs can oops or panic the client, which is High availability impact.