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CVE-2026-89669
nfsd: initialize copy-notify stateid before publishing it
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-2026-89669 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
nfsd4_copy_notify() finished initializing the cpntf state after nfs4_alloc_init_cpntf_state() had already linked it into the s2s_cp_stateids IDR and the parent's sc_cp_list, with cs_count == 1 (the membership reference) and none held for the caller. A racing OFFLOAD_CANCEL (crafted cl_id == nn->s2s_cp_cl_id plus the guessable so_id) could reach manage_cpntf_state() and free the entry, turning the caller's subsequent cpn_cnr_stateid read and cp_p_stateid/cp_p_clid writes into use-after-free. The owning clientid was also only recorded after publication, so it could not gate an ownership check in that window. Record cp_p_stateid and cp_p_clid inside nfs4_alloc_init_cpntf_state() before nfs4_init_cp_state() publishes the entry, and return it with an extra reference. The caller reads the stateid under that reference and drops it with nfs4_put_cpntf_state(); on a late error the laundromat reaps the entry.
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/nfs4proc.c
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
- 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
- 0.69%, higher than 52.0% 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 | 863b6e995665 |
| 5.6 | 5.15.221 | d18d36395d97 |
| 5.6 | 6.1.188 | 4415a692346a |
| 5.6 | 6.6.157 | 9caad13b7cfe |
| 5.6 | 6.12.109 | e08a3dcaca05 |
| 5.6 | 6.18.50 | a4d7fedcaaf3 |
| 5.6 | 7.2.4 | 4cdef96892f4 |
| 5.6 | 7.3 | 129643893b79 |
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 UAF is in nfsd COPY_NOTIFY (nfsd4_copy_notify/nfs4_alloc_init_cpntf_state). NFSv4.2 COPY_NOTIFY and a racing OFFLOAD_CANCEL are processed from compounds over TCP/2049 via nfsd4_proc_compound, so a remote NFS client reaches the published cpntf object over the network.
- AC:LAttack complexity, low
- The attacker controls both sides: one compound publishes the cpntf IDR entry via COPY_NOTIFY while a concurrent OFFLOAD_CANCEL uses the leaked nn->s2s_cp_cl_id and a cyclic guessable so_id to kfree it before initialization finishes; the race is retryable on multiple session slots with no condition outside attacker control.
- 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 drives COPY_NOTIFY and the concurrent OFFLOAD_CANCEL on its own connections; no victim user or administrator action on the NFS server is required at attack time.
- S:UScope, unchanged
- The use-after-free corrupts a kmalloc'd nfs4_cpntf_state in the host kernel's nfsd copy-notify tables. Impact stays in that kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.
- C:HConfidentiality impact, high
- After OFFLOAD_CANCEL kfree's the object (cs_count was 1), nfsd4_copy_notify memcpy's the freed cp_stateid.cs_stid into the RPC reply; reclaim of that kmalloc slab lets the attacker disclose kernel memory. Per kernel guidance a use-after-free is C:H.
- I:HIntegrity impact, high
- The same path then writes cp_p_stateid and cp_p_clid into the freed nfs4_cpntf_state, a use-after-free write primitive usable for heap corruption and control-flow hijacking. Per kernel guidance a use-after-free is I:H.
- A:HAvailability impact, high
- Use-after-free of nfs4_cpntf_state in an nfsd worker oopses or panics the NFS server even without full exploitation, and the attacker can repeat the concurrent RPC sequence to deny service.