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CVE-2026-93827
virtio-fs: avoid double-free on failed queue setup
Published 2026-09-24 (24 days ago) by the Linux kernel CNA. Subsystem fs/fuse. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-93827 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-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
virtio_fs_setup_vqs() allocates fs->vqs and fs->mq_map before calling virtio_find_vqs(). If virtio_find_vqs() fails, the error path frees both pointers and returns an error to virtio_fs_probe(). virtio_fs_probe() then drops the last kobject reference, and virtio_fs_ktype_release() frees fs->vqs and fs->mq_map again. This leaves dangling pointers in struct virtio_fs and can trigger a double-free during probe failure cleanup. Set fs->vqs and fs->mq_map to NULL immediately after kfree() in the virtio_fs_setup_vqs() error path so that the later kobject release sees an uninitialized state and kfree(NULL) becomes harmless. This can be reproduced when a broken virtio-fs device advertises more request queues than the transport actually provides. In that case virtio_find_vqs() fails while setting up the extra queue, and the probe path reaches the double-free cleanup sequence.
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/virtio_fs.c
- What this is
- VIRTIO FILE SYSTEMMAINTAINERS section matched on fs/fuse/virtio_fs.c · virtualization@lists.linux.dev · Supported
- Kernel module
- virtiofs
Check it on the machine
grep -wE 'CONFIG_FUSE_FS|CONFIG_VIRTIO_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 virtiofsPrints 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 switches
- CONFIG_FUSE_FS, CONFIG_VIRTIO_FS
- 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
- 2026-09-24 (24 days ago)source
- CVSS
- 8.4 high
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 3.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.9 | 6.12.111 | 3fbc5ee776fe |
| 6.9 | 6.18.53 | 20ef4739b329 |
| 6.9 | 7.2 | 6af3330ec5d5 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| 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:LAttack vector, local
- The triggering field is virtio_fs_config.num_request_queues, read by virtio_cread_le() in virtio_fs_setup_vqs() from virtio_fs_probe() via virtio_dev_probe() after virtio_pci_probe()/register_virtio_device() binds a VIRTIO_ID_FS device; those bytes come from local PCI/MMIO/vDPA config space, not a network protocol message.
- AC:LAttack complexity, low
- A device that advertises more request queues than it exposes makes virtio_find_vqs()->vp_setup_vq() fail (-EINVAL when index >= vp_modern_get_num_queues(), or -ENOENT on queue size 0); virtio_fs_setup_vqs() then kfree's fs->vqs and fs->mq_map and virtio_fs_probe() always kobject_put()s into the second free, with no race.
- PR:NPrivileges required, none
- virtio_fs_probe()/virtio_fs_setup_vqs() have no capable() or credential check; MODULE_DEVICE_TABLE(virtio, id_table) autoloads virtiofs and virtio_dev_probe() binds a VIRTIO_ID_FS device at enumeration or hotplug, so a malicious virtio-fs backend needs no account on the guest.
- UI:NUser interaction, none
- The double-free runs in the probe error path (virtio_fs_setup_vqs() failure, then kobject_put() into virtio_fs_ktype_release()) when the device appears; virtio_fs_add_instance() and a virtiofs mount are never reached, so no victim must mount or open anything.
- S:UScope, unchanged
- virtio_fs_ktype_release() double-frees the guest kernel kmalloc objects fs->vqs and fs->mq_map; that is device-to-guest heap corruption inside the same guest kernel, not a write into host virtiofsd or a KVM/IOMMU escape.
- C:HConfidentiality impact, high
- kfree(fs->vqs) and kfree(fs->mq_map) in virtio_fs_setup_vqs() leave dangling pointers that virtio_fs_ktype_release() frees again; a slab double-free of that virtio_fs_vq array and per-CPU mq_map lets those objects overlap so the attacker can read adjacent kernel heap.
- I:HIntegrity impact, high
- The same second kfree of fs->vqs and fs->mq_map corrupts the SLUB freelist for those kmalloc objects and is an arbitrary-free primitive, enabling heap overwrite and control-flow hijack in the guest kernel.
- A:HAvailability impact, high
- Double-free of fs->vqs and fs->mq_map in virtio_fs_ktype_release() after virtio_find_vqs() fails oopses or panics the guest during probe cleanup (KASAN invalid-free, SLUB poisoned-freelist BUG, or panic_on_oops).