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CVE-2026-89676
nfsd: fix stale s2s_cp_stateids IDR entry for async COPY
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-2026-89676 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| 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
For an async COPY, nfsd4_copy() called nfs4_init_copy_state() before dup_copy_fields(), so the s2s_cp_stateids IDR was pointed at &u->copy->cp_stateid -- memory in the per-rqstp COMPOUND buffer that is reused by the next request. dup_copy_fields() copies only the value into async_copy, so the IDR slot dangled at the transient buffer for the whole background copy. Any IDR walker then dereferences reused request memory: the laundromat reads cs_type from it and, if the bytes look like an expired NFS4_COPYNOTIFY_STID, follows into refcount_dec()/idr_remove()/kfree() on garbage; manage_cpntf_state() has the same exposure via idr_find(). Duplicate the fields first, then register the stateid on the stable async_copy. result->cb_stateid is unchanged.
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
- 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
- 0.46%, higher than 38.2% 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 |
|---|---|---|
| 4.20 | 6.12.111 | 7aa34ea78f74 |
| 4.20 | 6.18.50 | 9b4e5e9ba5ae |
| 4.20 | 7.2.4 | 14b978e8d05c |
| 4.20 | 7.3 | d0beaee498e1 |
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
- The dangling s2s_cp_stateids pointer is installed by nfsd4_copy in the in-kernel NFSv4.2 server; a remote client reaches it over TCP/2049 via COMPOUND RPCs (EXCHANGE_ID, CREATE_SESSION, OPEN, then async COPY).
- AC:LAttack complexity, low
- The attacker reliably creates the stale IDR entry with async COPY, then either reuses that nfsd thread's COMPOUND iops buffer with further requests or sends a >8-op compound so the vcalloc'd ops array is kvfree_rcu'd, and later walks the IDR via OFFLOAD_CANCEL/READ or the laundromat; no condition outside attacker control is required.
- PR:NPrivileges required, none
- Typical nfsd deployments use AUTH_SYS or AUTH_NULL with IP-based exports, so a remote peer that can reach the export can create an NFSv4.2 session, OPEN readable and writable files, and issue async COPY without a local account or capability on the NFS server.
- UI:NUser interaction, none
- Exploitation requires only attacker-sent NFS RPCs against a running nfsd export; no victim user action such as mounting a filesystem or opening a local file on the server is required.
- S:UScope, unchanged
- The stale IDR dereference corrupts kernel nfsd copy and copy-notify state on the NFS server host and does not cross a VM, IOMMU, or sandbox boundary.
- C:HConfidentiality impact, high
- The IDR retains a pointer into reused per-rqstp COMPOUND memory or a kvfree_rcu'd ops array; the laundromat and manage_cpntf_state then read cs_type and adjacent fields from attacker-controlled reused or sprayed memory, a use-after-free disclosure primitive.
- I:HIntegrity impact, high
- When reused bytes look like an expired NFS4_COPYNOTIFY_STID, the laundromat and manage_cpntf_state perform list_del, refcount_dec, and kfree on the garbage object, a use-after-free write/free primitive that enables heap corruption and control-flow hijacking.
- A:HAvailability impact, high
- kfree or list_del on the dangling COMPOUND buffer or sprayed slab oopses or panics nfsd worker threads, and the attacker can repeat async COPY plus IDR walks to take down the NFS server host.