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CVE-2026-89697
nfsd: add fh_want_write() for early-verified SETATTR in nfsd_proc_setattr()
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem fs/nfsd. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-89697 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
The BOTH_TIME_SET branch calls fh_verify() early so setattr_prepare() can inspect the dentry. This causes nfsd_setattr() to skip fh_want_write(), so notify_change() runs without a mount write reference. Add the missing fh_want_write() call after the early fh_verify().
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/nfsproc.c
- What this is
- KERNEL NFSD, SUNRPC, AND LOCKD SERVERSMAINTAINERS section matched on fs/nfsd/ · linux-nfs@vger.kernel.org · Supported
- Kernel module
- none to look for. The file would have gone into nfsd, and Debian does not compile it into that module, so finding nfsd in lsmod would say nothing about this CVE.
Check it on the machine
grep -wE 'CONFIG_NFSD|CONFIG_NFSD_V2' /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.
Show whether Debian builds this, per release
Debian does not build this code. In 5 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12n
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_NFSD, CONFIG_NFSD_V2
- 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
- 9.1 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.70%, higher than 52.1% 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 |
|---|---|---|
| 4.2 | 5.10.270 | 3eec9d791968 |
| 4.2 | 5.15.221 | 9229d824b938 |
| 4.2 | 6.1.188 | 215030513488 |
| 4.2 | 6.6.157 | d823bf9285cd |
| 4.2 | 6.12.109 | 15ca3b64a69c |
| 4.2 | 6.18.50 | 533964d420d3 |
| 4.2 | 7.2.4 | c4a409b86a92 |
| 4.2 | 7.3 | 4e475be769aa |
| 3.18.46 | 0 | 0 |
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 bug is in nfsd_proc_setattr(), the in-kernel NFSv2 SETATTR handler. A remote client reaches it by sending an NFSv2 SETATTR RPC over TCP/UDP port 2049 with both atime and mtime set, so no local access to the server is required.
- AC:LAttack complexity, low
- Crafting SETATTR with ATTR_ATIME_SET|ATTR_MTIME_SET and equal timestamps deterministically takes the early fh_verify() path so nfsd_setattr() skips fh_want_write(). The attacker fully controls the RPC; no race or uninfluenced memory layout is required.
- PR:NPrivileges required, none
- Default nfsd exports accept AUTH_SYS and AUTH_NULL with no cryptographic authentication, so the client asserts uid/gid. Any host permitted by the export list can issue SETATTR; this matches prior nfsd CNA scoring as PR:N.
- UI:NUser interaction, none
- The attacking NFS client issues the SETATTR RPC itself. No administrator or end-user action on the server is required.
- S:UScope, unchanged
- notify_change() without a mount write reference affects only the exported filesystem in the same kernel security authority. No VM, IOMMU, or sandbox boundary is crossed.
- C:NConfidentiality impact, none
- The defect is a missing mnt_want_write()/sb_start_write() around notify_change() and commit_metadata(). It does not leak kernel memory, pointers, or file contents beyond ordinary authorized NFS access.
- I:HIntegrity impact, high
- nfsd_permission's read-only check does not cover freeze state, so SETATTR including ATTR_SIZE truncate, mode, and ownership updates proceeds on a frozen export and in a remount-ro race, letting a client mutate files and corrupt snapshots when writes should be blocked.
- A:HAvailability impact, high
- Skipping freeze protection lets setattr run during fsfreeze, which can deadlock (inode_lock versus sb_start_write ordering), trigger filesystem withdraw/asserts such as GFS2 adding buffers while frozen, and hang or crash the nfsd thread.