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CVE-2026-89684
nfsd: fix cpntf publish race in nfs4_init_cp_state
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem fs/nfsd. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89684 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
nfs4_alloc_init_cpntf_state() published the new cpntf entry into the s2s_cp_stateids IDR (with cs_type set) in one s2s_cp_lock section, then took the lock again to list_add() it onto p_stid->sc_cp_list. In the gap the entry is reachable by so_id but cp_list is still {NULL,NULL} from kzalloc. A racing OFFLOAD_CANCEL (so_id is echoed to the client as cnr_stateid, so any NFSv4.2 client can drive it) reaches manage_cpntf_state() -> _free_cpntf_state_locked() and does list_del() on the zeroed list_head, oopsing the server. Fold the cs_type assignment and the list_add() into the same critical section as idr_alloc_cyclic(), so a concurrent lookup either misses the entry or sees a fully linked cp_list. INIT_LIST_HEAD() the entry after allocation and switch _free_cpntf_state_locked() to list_del_init() so a stale unlink is a no-op. nfs4_init_copy_state() passes NULL p_stid and skips the list_add, preserving NFS4_COPY_STID semantics.
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/nfsd/nfs4state.c
- What this is
- KERNEL NFSD, SUNRPC, AND LOCKD SERVERSMAINTAINERS section matched on fs/nfsd/ · linux-nfs@vger.kernel.org · Supported
- Kernel module
- nfsd
Check it on the machine
grep -wE 'CONFIG_NFSD|CONFIG_NFSD_V4' /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 nfsdPrints 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 switches
- CONFIG_NFSD, CONFIG_NFSD_V4
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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/nfsd
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.6 | 5.10.270 | 63e18fc65587 |
| 5.6 | 5.15.221 | 6ac469a274e3 |
| 5.6 | 6.1.188 | 8eeca993357a |
| 5.6 | 6.6.157 | bfeac42d9074 |
| 5.6 | 6.12.109 | 21d6c5957f5c |
| 5.6 | 6.18.50 | a631a26a8777 |
| 5.6 | 7.2.4 | c7270f62e7a0 |
| 5.6 | 7.3 | be3a5c1d857b |
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
- The flaw is in nfsd NFSv4.2 COPY_NOTIFY/OFFLOAD_CANCEL (nfsd4_copy_notify, nfs4_alloc_init_cpntf_state, manage_cpntf_state). Compounds reach nfsd4_proc_compound via svc_process on TCP/2049, so a remote NFS client triggers the published cpntf IDR entry over the network.
- AC:LAttack complexity, low
- The attacker drives both sides: COPY_NOTIFY publishes the cpntf into s2s_cp_stateids while a concurrent OFFLOAD_CANCEL uses the leaked s2s_cp_cl_id and cyclic so_id to list_del the still-zeroed cp_list. The window is retryable on multiple session slots with no victim-controlled state.
- PR:NPrivileges required, none
- Default AUTH_SYS/AUTH_NULL nfsd exports do no cryptographic authentication. Any host allowed by the export ACL can EXCHANGE_ID/CREATE_SESSION, OPEN a readable file, and issue COPY_NOTIFY and OFFLOAD_CANCEL; no local account or capability on the NFS server is required.
- UI:NUser interaction, none
- The attacking NFS client sends COPY_NOTIFY and the concurrent OFFLOAD_CANCEL itself; no victim user or administrator action on the NFS server is required at attack time.
- S:UScope, unchanged
- list_del of the uninitialized cp_list oopses an nfsd worker in the host kernel copy-notify tables. Impact stays in that kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.
- C:NConfidentiality impact, none
- The race is list_del on a kzalloc'd nfs4_cpntf_state.cp_list still {NULL,NULL}, a NULL-pointer dereference in __list_del. It oopses without reading kernel memory or providing an information-disclosure primitive.
- I:NIntegrity impact, none
- The only write is next->prev/prev->next through NULL list pointers from kzalloc; a remote NFS client cannot map the NULL page, so this is not a kernel write or control-flow hijack primitive.
- A:HAvailability impact, high
- list_del on the zeroed list_head oopses or panics the nfsd thread (and can leak s2s_cp_lock). The attacker can repeat the concurrent COMPOUND sequence to deny NFS service and take down the server.