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CVE-2026-53381
virtiofs: fix UAF on submount umount
Published 2026-07-19 (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-2026-53381 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 | fixed | 6.1.177-1 | Update the kernel and reboot. Fixed in 6.1.177-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.95-1 | Update the kernel and reboot. Fixed in 6.12.95-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.14-1 | Update the kernel and reboot. Fixed in 7.0.14-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.14-1 | Update the kernel and reboot. Fixed in 7.0.14-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
iput() called from fuse_release_end() can Oops if the super block has already been destroyed. Normally this is prevented by waiting for num_waiting to go down to zero before commencing with super block shutdown. This only works, however, for the last submount instance, as the wait counter is per connection, not per superblock. Revert to using synchronous release requests for the auto_submounts case, which is virtiofs only at this time.
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/file.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, sidy
- 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
- 2026-07-19 (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
- 0.14%, higher than 2.9% 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 |
|---|---|---|
| 5.10.246 | 5.10.260 | 607a1d4c42f6 |
| 5.15.196 | 5.15.211 | 1cc0e3a0c649 |
| 6.1.158 | 6.1.177 | 0b809199ff87 |
| 6.6.115 | 6.6.144 | 2181a09ba980 |
| 6.12.54 | 6.12.95 | 97c4691653d1 |
| 6.18 | 6.18.37 | 2abfd3ffbd94 |
| 6.18 | 7.0.14 | 39a2b95e0086 |
| 6.18 | 7.1.2 | e09412a714bc |
| 6.18 | 7.2 | 06b41351779e |
| 6.17.4 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4717-1 | 2026-08-05 | bullseye 5.10.262-1 | tracker |
| DLA-4700-1 | 2026-07-26 | bullseye 6.1.177-1~deb11u1 | 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
- The bug is reached through local VFS operations (open/write/close) on a virtiofs mount with FUSE submounts; exploitation is in the guest FUSE client during file release and submount umount, not via remote network packets.
- AC:LAttack complexity, low
- This is a use-after-free where the attacker controls file close (async FUSE RELEASE) and can drive or coincide with submount umount; Kata Containers reproduces it reliably with virtiofsd --announce-submounts (default).
- PR:LPrivileges required, low
- An unprivileged local process with access to the virtiofs mount can trigger it; virtiofs defaults to allow_other and normal POSIX permissions, and no real root or init-namespace capabilities are required.
- UI:NUser interaction, none
- Exploitation needs no victim interaction beyond the attacker (or their container workload) performing normal filesystem I/O while submount teardown occurs during pod/container lifecycle.
- S:UScope, unchanged
- Impact stays within the guest kernel security boundary (crash or guest kernel compromise); it does not by itself cross a VM/host or IOMMU boundary.
- C:HConfidentiality impact, high
- The flaw is a use-after-free in fuse_release_end() calling iput() on an inode after its superblock is destroyed, which can be turned into arbitrary kernel memory read via heap manipulation.
- I:HIntegrity impact, high
- Use-after-free on a struct inode in the kernel heap provides a standard path to controlled memory corruption, heap spraying, and arbitrary write or code execution in kernel context.
- A:HAvailability impact, high
- Confirmed kernel general protection fault/oops in iput() from fuse_release_end during virtio_fs request completion, and UAF bugs inherently threaten kernel stability even without full exploitation.