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CVE-2026-64061

netfs: Fix early put of sink folio in netfs_read_gaps()

9.8 EPSS 0.7% AV:N

Published 2026-07-19 (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-2026-64061 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	fixed	6.12.94-1	Update the kernel and reboot. Fixed in 6.12.94-1. 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.

The vulnerability

What the bug is

Fix netfs_read_gaps() to release the sink page it uses after waiting for the request to complete. The way the sink page is used is that an ITER_BVEC-class iterator is created that has the gaps from the target folio at either end, but has the sink page tiled over the middle so that a single read op can fill in both gaps. The bug was found by KASAN detecting a UAF on the generic/075 xfstest in the cifsd kernel thread that handles reception of data from the TCP socket: BUG: KASAN: use-after-free in _copy_to_iter+0x48a/0xa20 Write of size 885 at addr ffff888107f92000 by task cifsd/1285 CPU: 2 UID: 0 PID: 1285 Comm: cifsd Not tainted 7.0.0 #6 PREEMPT(lazy) Call Trace: dump_stack_lvl+0x5d/0x80 print_report+0x17f/0x4f1 kasan_report+0x100/0x1e0 kasan_check_range+0x10f/0x1e0 __asan_memcpy+0x3c/0x60 _copy_to_iter+0x48a/0xa20 __skb_datagram_iter+0x2c9/0x430 skb_copy_datagram_iter+0x6e/0x160 tcp_recvmsg_locked+0xce0/0x1130 tcp_recvmsg+0xeb/0x300 inet_recvmsg+0xcf/0x3a0 sock_recvmsg+0xea/0x100 cifs_readv_from_socket+0x3a6/0x4d0 [cifs] cifs_read_iter_from_socket+0xdd/0x130 [cifs] cifs_readv_receive+0xaad/0xb10 [cifs] cifs_demultiplex_thread+0x1148/0x1740 [cifs] kthread+0x1cf/0x210

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

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, sidm

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: 2026-07-19 (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: 0.65%, higher than 50.2% 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	6.12.92	2a39d49c8d97
6.12	6.18.34	d4f4bc87c765
6.12	7.0.11	412e8bad4896
6.12	7.1	3e5dd91b87a8

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 UAF write occurs in the CIFS client kernel thread while copying SMB read-response data received over TCP; a compromised or malicious network filesystem server can supply attacker-controlled payload once a client performs normal buffered read/write on a mounted share.
AC:LAttack complexity, low: The bug is deterministic—folio_put(sink) always runs before netfs_wait_for_read() completes—so an attacker who can create a dirty streaming-write folio and then read it reliably triggers the UAF without winning a race.
PR:NPrivileges required, none: A remote malicious/compromised SMB/NFS/9p/Ceph server attacker needs no local privileges on the victim; exploitation requires only ordinary file access on an existing network mount, not root or special capabilities.
UI:NUser interaction, none: No special victim interaction beyond normal file read/write operations on a mounted network filesystem; persistent automounts and server-driven workloads make mount-time interaction unnecessary for exploitation.
S:UScope, unchanged: Impact is kernel heap memory corruption within the same kernel security domain; it does not cross VM, container, or IOMMU boundaries.
C:HConfidentiality impact, high: Use-after-free of a page-cache folio enables heap grooming and arbitrary kernel memory read primitives; UAF class bugs are scored High for confidentiality per kernel CNA guidance.
I:HIntegrity impact, high: The UAF is a write primitive—KASAN reported an 885-byte write of network-supplied data into freed memory—enabling controlled heap corruption and potential code execution.
A:HAvailability impact, high: UAF during network I/O can cause kernel oops/panic and denial of service to all workloads on the host; UAF bugs are scored High for availability per kernel CNA guidance.