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CVE-2026-64266
fuse: re-lock request before returning from fuse_ref_folio()
Published 2026-07-25 (3 months ago) by the Linux kernel CNA. Subsystem fs/fuse. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64266 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-4720-1 · 2026-08-05 · text | 6.1.180-1 | Update the kernel and reboot. DLA-4720-1 shipped the fix on 2026-08-05, in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.96-1 | Update the kernel and reboot. Fixed in 6.12.96-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
fuse_ref_folio() unlocks the request but does not re-lock it before returning. fuse_chan_abort() can end the request and the async end callback (eg fuse_writepage_free()) can free the args while the subsequent copy chain logic after fuse_ref_folio() accesses them, leading to use-after-free issues. Fix this by locking the request in fuse_ref_folio() before returning.
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/fuse/dev.c
- What this is
- FUSE FILESYSTEM [CORE]MAINTAINERS section matched on fs/fuse/ · fuse-devel@lists.linux.dev · Supported
- Kernel module
- fuse
Check it on the machine
grep -w CONFIG_FUSE_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 fusePrints 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 code. Every release below compiles the affected file into the kernels it ships.
- bookwormm
- trixie, forky, sid, bookworm · linux-6.12y
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_FUSE_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
- 2026-07-25 (3 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 5.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/fuse
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.35 | 5.10.261 | 1f9156714592 |
| 2.6.35 | 5.15.212 | 5630da218a45 |
| 2.6.35 | 6.1.178 | 1ca605cfa593 |
| 2.6.35 | 6.6.145 | 0e4a5a000123 |
| 2.6.35 | 6.12.96 | e6aa539720c3 |
| 2.6.35 | 6.18.39 | be353caffa86 |
| 2.6.35 | 7.1.4 | 65a1c2551f7e |
| 2.6.35 | 7.2 | b5befa80fdbe |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DLA-4723-1 | 2026-08-07 | bullseye 6.1.180-1~deb11u1 | tracker |
| DLA-4720-1 | 2026-08-05 | bookworm 6.1.180-1 | tracker |
| DLA-4717-1 | 2026-08-05 | bullseye 5.10.262-1 | 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:LAttack vector, local
- A local attacker reaches the flaw by serving a self-created FUSE mount and invoking splice() on its associated /dev/fuse descriptor.
- AC:LAttack complexity, low
- The attacker controls writeback generation, splice processing, and concurrent connection abort, allowing repeated attempts at the race without an uncontrollable prerequisite.
- PR:LPrivileges required, low
- FUSE supports user-namespace mounts, and an unprivileged mount owner can operate /dev/fuse and abort their own connection without init-namespace root.
- UI:NUser interaction, none
- The attacker can create and exercise their own FUSE connection without any victim action.
- S:UScope, unchanged
- Exploitation compromises the kernel within the same operating-system security authority and does not inherently cross a virtualization boundary.
- C:HConfidentiality impact, high
- The freed argument and folio arrays are subsequently dereferenced, permitting attacker-influenced stale folio pointers and potential arbitrary kernel-memory disclosure through pipe buffers.
- I:HIntegrity impact, high
- Heap reclamation can replace the freed folio pointers and loop metadata, enabling attacker-directed memory or refcount operations that may support arbitrary writes and kernel code execution.
- A:HAvailability impact, high
- The repeatable use-after-free and invalid folio operations can cause an oops, panic, or other complete system failure.