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CVE-2026-64216

netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages()

9.8 EPSS 0.5% AV:N

Published 2026-07-24 (3 months ago) by the Linux kernel CNA. Subsystem fs/netfs. Debian urgency: unimportant.

What to do, per Debian release

Debian's own status for CVE-2026-64216 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	not affected	6.1.190-1	Nothing to do. bookworm never shipped the vulnerable code.
Debian 13trixie	fixedDSA-6477-1 · 2026-08-29 · text	6.12.107-1	Update the kernel and reboot. DSA-6477-1 shipped the fix on 2026-08-29, in 6.12.107-1. A running kernel keeps the old code until the machine restarts.
Debian 14forky	fixed	7.0.12-1	Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts.
Debian unstablesid	fixed	7.0.12-1	Update the kernel and reboot. Fixed in 7.0.12-1. 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

netfs_unlock_abandoned_read_pages(rreq) accesses the index of the folios it is wanting to unlock and compares that to rreq->no_unlock_folio so that it doesn't unlock a folio being read for netfs_perform_write() or netfs_write_begin(). However, given that netfs_unlock_abandoned_read_pages() is called _after_ NETFS_RREQ_IN_PROGRESS is cleared, the one folio that it's not allowed to dereference is the one specified by ->no_unlock_folio as ownership immediately reverts to the caller. Fix this by storing the folio pointer instead and using that rather than the index. Also fix netfs_unlock_read_folio() where the same applies.

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/netfs/buffered_read.c
fs/netfs/read_collect.c
fs/netfs/read_retry.c
include/linux/netfs.h

What this is: FILESYSTEMS [NETFS LIBRARY]MAINTAINERS section matched on fs/netfs/ · netfs@lists.linux.dev · Supported
Kernel module: netfs

Check it on the machine

grep -w CONFIG_NETFS_SUPPORT /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 netfs

Prints 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_NETFS_SUPPORT

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

Debian tracker CVE record NVD kernel CNA record

Signals

Published: 2026-07-24 (3 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: 0.46%, higher than 38.2% of all CVEssource
CISA KEV: not listedthe KEV catalogue
Debian urgency: unimportantsource
Subsystem: fs/netfs

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
6.12	6.12.106	d4ae8dba90b8
6.12	6.18.34	6080fa3ecfbb
6.12	7.0.11	3866d015f33a
6.12	7.1	dbe556972100

Debian advisories

Advisory	Date	Shipped to	Debian
DLA-4788-1	2026-09-19	bookworm 6.12.107-1~deb12u1	tracker
DSA-6477-1	2026-08-29	trixie 6.12.107-1	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 vulnerable read-for-write completion is used by network filesystem clients including Ceph, SMB, 9P, and AFS. A malicious filesystem peer can induce failed or malformed reads and control completion timing.
AC:LAttack complexity, low: Partial buffered writes and concurrent invalidation can repeatedly trigger the race, with an adjacent bug reproducing approximately 30% of repeated attempts. The attacker can influence completion, reuse, and retry timing.
PR:NPrivileges required, none: A malicious filesystem server requires no privileges on the victim client; mount and session credentials belong to the victim.
UI:NUser interaction, none: Once the network filesystem is mounted, ordinary or automated writes can exercise the vulnerable path without further human action.
S:UScope, unchanged: The UAF corrupts resources within the host kernel's existing security authority and does not inherently cross a VM, IOMMU, or sandbox boundary.
C:HConfidentiality impact, high: The stale folio can be freed and reused, and premature unlocking of a replacement page can expose page-cache or kernel contents.
I:HIntegrity impact, high: If the folio is reused, folio_unlock() can toggle PG_locked on an unrelated page, enabling concurrent memory corruption and potentially code execution.
A:HAvailability impact, high: The condition can trigger a VM_BUG_ON_FOLIO kernel crash; incorrect PG_locked state can also cause permanent page-lock waits and system hangs.