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CVE-2026-90149
NFSv4/flexfiles: fix NULL dereference for NFSv4.0 data servers
Published 2026-09-17 (31 days 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-2026-90149 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 | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| 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. |
The vulnerability
What the bug is
flexfiles accepts NFSv4.0 data servers, but two NFSv4 code paths assume the data server client has a session. Unlike NFSv4.1+, an NFSv4.0 client has no session (clp->cl_session is NULL; it uses clp->cl_slot_tbl), so I/O to a v4.0 flexfiles DS oopses: - nfs4_init_ds_session() dereferences clp->cl_session->session_state while seeding the DS lease. It also only seeds cl_lease_time when NFS4_SESSION_INITING is set; without a session that never happens, so cl_lease_time stays 0 and nfs4_renew_state() busy-loops, requeuing every 5 seconds. Seed the lease whenever there is no session and return before touching session state. - ff_layout_async_handle_error_v4() dereferences clp->cl_session->fc_slot_table on every DS I/O error. Fall back to the v4.0 transport slot table (clp->cl_slot_tbl) when there is no session.
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/flexfilelayout/flexfilelayout.c
fs/nfs/nfs4session.c
- What this is
- NFS, SUNRPC, AND LOCKD CLIENTSMAINTAINERS section matched on fs/nfs/ · linux-nfs@vger.kernel.org · Maintained
- Kernel module
- nfs_layout_flexfiles
Check it on the machine
grep -wE 'CONFIG_NFS_FS|CONFIG_PNFS_FLEXFILE_LAYOUT' /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 nfs_layout_flexfilesPrints 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, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NFS_FS, CONFIG_PNFS_FLEXFILE_LAYOUT
- 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
- 2026-09-17 (31 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
- 0.59%, higher than 47.2% 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 |
|---|---|---|
| 4.12 | 6.18.52 | 163c16e01f53 |
| 4.12 | 7.2.6 | 436a214514e2 |
| 4.12 | 7.3 | 2b03ebbf8d5e |
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
- A malicious NFSv4.1 MDS sets version=4 and minor_version=0 in the flexfiles GETDEVICEINFO device-addr body; nfs4_ff_alloc_deviceid_node() accepts that pair, nfs4_set_ds_client() builds a session-less v4.0 nfs_client, and nfs4_init_ds_session() then crashes on DS connect. GETDEVICEINFO is NFS/RPC over TCP.
- AC:LAttack complexity, low
- nfs4_ff_alloc_deviceid_node() explicitly allows an NFSv4.0 DS (version==4 && minor_version<3). The MDS sets those two GETDEVICEINFO XDR words, and the next read/write that reaches nfs4_ff_layout_prepare_ds() → nfs4_init_ds_session() dereferences the NULL cl_session with no race.
- PR:NPrivileges required, none
- The attacker is the remote MDS (or an on-path injector of GETDEVICEINFO replies) and needs no account or capability on the victim client; the client authenticates to the server, not the reverse.
- UI:NUser interaction, none
- On an already-mounted pNFS flexfiles share, ordinary file I/O drives LAYOUTGET then GETDEVICEINFO; the MDS can return a v4.0 DS in that GETDEVICEINFO and nfs4_init_ds_session() oopses with no further victim action such as mounting a new image.
- S:UScope, unchanged
- The NULL dereference oopses the NFS client kernel itself and does not cross a VM, IOMMU, or other security-authority boundary.
- C:NConfidentiality impact, none
- nfs4_init_ds_session() loads clp->cl_session->session_state when cl_session is NULL, a pure NULL-pointer fault at a low offset of struct nfs4_session, with no out-of-bounds read or other disclosure.
- I:NIntegrity impact, none
- The same NULL load of cl_session (and cl_session->fc_slot_table in ff_layout_async_handle_error_v4) faults before any store; this is not a UAF, overflow, or type confusion that could yield a write primitive.
- A:HAvailability impact, high
- Dereferencing the NULL cl_session in nfs4_init_ds_session() on DS connect, or cl_session->fc_slot_table in ff_layout_async_handle_error_v4 on a DS I/O error, produces a kernel oops that takes down the client.