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CVE-2026-90151
NFSv4: remove callback IDR entry on client allocation failure
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-2026-90151 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_client() allocates an NFSv4.0 callback identifier before it finishes setting up the client. If any later initialization step fails, the error path frees the nfs_client directly with nfs_free_client(). That bypasses nfs_put_client(), which is where the callback IDR entry is removed during normal teardown. A failed allocation can therefore leave cb_ident_idr pointing at a freed nfs_client. A later NFSv4.0 callback lookup by cb_ident would find the stale pointer and take a reference to it. Make the callback IDR removal helper callable by the allocation failure path, and remove the callback identifier before freeing the client. This was found by a local static-analysis checker for publish-before-free lifetime bugs and confirmed by manual inspection.
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/client.c
fs/nfs/internal.h
fs/nfs/nfs4client.c
- What this is
- NFS, SUNRPC, AND LOCKD CLIENTSMAINTAINERS section matched on fs/nfs/ · linux-nfs@vger.kernel.org · Maintained
- Kernel module
- nfs
Check it on the machine
grep -w CONFIG_NFS_FS /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 nfsPrints 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 switch
- CONFIG_NFS_FS
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
- 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
- 0.74%, higher than 53.7% 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 |
|---|---|---|
| 2.6.38 | 5.10.270 | 68c721391b76 |
| 2.6.38 | 5.15.221 | 9bfdd0f59130 |
| 2.6.38 | 6.1.188 | 7c4812eb96bd |
| 2.6.38 | 6.6.157 | fc95ca82d5ae |
| 2.6.38 | 6.12.110 | 80b1c3d5a881 |
| 2.6.38 | 6.18.52 | 3f2387e8bfbc |
| 2.6.38 | 7.2.6 | 5891c03e1509 |
| 2.6.38 | 7.3 | d05c2007b3d8 |
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
- nfs4_find_client_ident() is called from nfs4_callback_compound() with hdr_arg.cb_ident taken by decode_compound_hdr_arg() from an NFSv4.0 CB_COMPOUND on the TCP callback listener that nfs4_callback_up_net() binds to INADDR_ANY via svc_xprt_create(); the remote peer supplies that identifier over routable TCP.
- AC:LAttack complexity, low
- A malicious NFSv4.0 server keeps the callback service up, then forces a later nfs4_alloc_client() to fail after nfs_get_cb_ident_idr() by making rpc_create()/rpc_ping() fail in nfs_create_rpc_client() (nfs4_create_referral_server or nfs4_update_server to an RST-ing address), then sends CB_COMPOUND with the next sequential idr id; no uncontrolled race is required.
- PR:NPrivileges required, none
- nfs4_find_client_ident() runs in nfs4_callback_compound() before check_gss_callback_principal(), and nfs_callback_authenticate() accepts RPC_AUTH_UNIX for CB_COMPOUND, so the peer needs no account or capability on the victim client.
- UI:NUser interaction, none
- The same peer returns NFS4ERR_MOVED so nfs4_schedule_migration_recovery() or a LOOKUP referral (nfs4_create_referral_server) runs nfs4_alloc_client() from the state manager or automount, then sends the CB_COMPOUND itself; no extra victim mount dialog or file-open is required.
- S:UScope, unchanged
- The UAF is of an nfs_client published in cb_ident_idr and freed by nfs_free_client(); impact stays in the host kernel and does not cross a VM, IOMMU, or guest/host boundary.
- C:HConfidentiality impact, high
- nfs4_find_client_ident() does refcount_inc(&clp->cl_count) on the nfs_client that nfs_free_client() already kfree_rcu'd, so a stale cb_ident_idr pointer remains; reclaim of that heap object yields an arbitrary kernel read, as with other kernel UAFs.
- I:HIntegrity impact, high
- The same stale-IDR lookup is a use-after-free write (refcount_inc, then nfs_put_client list_del and field access in check_gss_callback_principal/process_op); spraying the freed nfs_client enables arbitrary write and control-flow hijack.
- A:HAvailability impact, high
- refcount_inc on the kfree_rcu'd nfs_client, or later dereference of cl_rpcclient left as ERR_PTR(-EINVAL) when nfs_create_rpc_client() failed, causes a kernel oops/panic even without a full exploit.