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CVE-2026-74730
NFS: Pin the 'struct nfs_server' during a FREE_STATEID call
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem fs/nfs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74730 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Dan Aloni reports that he was able to hit a use-after-free bug if a FREE_STATEID operation gets delayed for whatever reason. Fix this by bumping the refcount of the 'struct nfs_server' object for the duration of the FREE_STATEID so it doesn't get cleaned up from underneath us while operations are still in flight.
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/nfs/nfs4proc.c
- What this is
- NFS, SUNRPC, AND LOCKD CLIENTSMAINTAINERS section matched on fs/nfs/ · linux-nfs@vger.kernel.org · Maintained
- Kernel module
- nfsv4
Check it on the machine
grep -wE 'CONFIG_NFS_FS|CONFIG_NFS_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 nfsv4Prints 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_NFS_FS, CONFIG_NFS_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
- 2026-08-22 (2 months 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 42.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/nfs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 3.10 | 5.10.265 | ed2f92ce2fc4 |
| 3.10 | 5.15.216 | d858ab09e787 |
| 3.10 | 6.1.183 | af62f1af182d |
| 3.10 | 6.6.152 | caee6a68ffaa |
| 3.10 | 6.12.104 | ed1161ab6239 |
| 3.10 | 6.18.45 | d71dfffa512e |
| 3.10 | 7.1.9 | 80ed3d762628 |
| 3.10 | 7.2 | cf616096a0f3 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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 bug is in the NFSv4 client FREE_STATEID path: nfs41_free_stateid_prepare/done/release use a freed struct nfs_server while handling async RPC completions driven by NFSv4 replies from the mounted server and by server-initiated CB_RECALL/CB_RECALLANY callbacks on the NFS backchannel.
- AC:LAttack complexity, low
- The attacker controls both sides of the race: they provoke FREE_STATEID via revocation responses or callbacks, keep it in flight with NFS4ERR_DELAY, and time nfs_server teardown via user-mount umount, automount idle expiry, or the concurrent stateid cleanup that runs during umount itself.
- PR:NPrivileges required, none
- A malicious or compromised NFSv4 server needs no account or elevated capability on the victim client once an NFSv4.1+ mount exists; FREE_STATEID is issued automatically during server-driven stateid revocation handling without any client-side privileges at exploit time.
- UI:NUser interaction, none
- After an NFS mount exists (boot-time, autofs, or Kubernetes volumes are common), no further victim action is needed: the attacker drives recall/revocation on the wire and mount teardown follows from automated autofs expiry or attacker-controlled umount on a user-mounted export.
- S:UScope, unchanged
- The use-after-free corrupts kernel heap within the NFS client on the same host; it is a standard kernel memory-safety bug, not a VM escape, container breakout, or IOMMU/DMA boundary crossing.
- C:HConfidentiality impact, high
- Freed struct nfs_server objects are kmalloc'd and callbacks dereference nfs_client, rpc_clnt, and super_block fields after nfs_free_server/call_rcu, giving a classic UAF read primitive over attacker-influenced heap contents including function pointers.
- I:HIntegrity impact, high
- UAF on struct nfs_server exposes destroy hooks, RPC client handles, and client/session state pointers that an attacker can reschedule via heap grooming, yielding write and control-flow primitives typical of NFS client heap corruption bugs.
- A:HAvailability impact, high
- Use of a freed nfs_server in RPC prepare/done/release paths causes kernel oops or panic; Dan Aloni demonstrated reliable reproduction, and UAFs in this path crash hosts even when not fully weaponized.