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CVE-2026-97415
btrfs: tree-checker: validate names in ROOT_REF and ROOT_BACKREF
Published 2026-09-24 (24 days ago) by the Linux kernel CNA. Subsystem fs/btrfs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-97415 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-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| 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
ROOT_REF and ROOT_BACKREF items contain a struct btrfs_root_ref followed by the subvolume name. Several readers assume that this layout is already valid and then use the on-disk name length directly. A corrupted item can therefore make those readers address bytes outside the item, and BTRFS_IOC_GET_SUBVOL_INFO can copy too many bytes into its fixed-size UAPI name buffer. Validate ROOT_REF and ROOT_BACKREF items in tree-checker before any reader uses them. Reject records that do not contain a non-empty name, whose name_len does not exactly describe the remaining item payload, or whose name exceeds BTRFS_NAME_LEN. For BTRFS_IOC_GET_SUBVOL_INFO, copy only the validated on-disk name_len instead of deriving the copy length from the item size. The ioctl result is zeroed when allocated. That leaves the existing trailing zero byte untouched.
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/btrfs/ioctl.c
fs/btrfs/tree-checker.c
- What this is
- BTRFS FILE SYSTEMMAINTAINERS section matched on fs/btrfs/ · linux-btrfs@vger.kernel.org · Maintained
- Kernel module
- btrfs
Check it on the machine
grep -w CONFIG_BTRFS_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 btrfsPrints 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_BTRFS_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
- 2026-09-24 (24 days 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
- 0.13%, higher than 2.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/btrfs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.18 | 6.1.189 | 1370badf6b82 |
| 4.18 | 6.6.158 | ba6c4fc66285 |
| 4.18 | 6.12.111 | 9154542070ca |
| 4.18 | 6.18.53 | 74f577c722c9 |
| 4.18 | 7.2 | 0af37c217edf |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| 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 attacker-controlled bytes are the on-disk BTRFS_ROOT_BACKREF_KEY item (struct btrfs_root_ref plus the following name) in the tree of tree roots. After that image is mounted, ioctl(BTRFS_IOC_GET_SUBVOL_INFO) reaches _btrfs_ioctl_get_subvol_info() via btrfs_ioctl() and read_extent_buffer()s the item; no SMB/NFS/packet field carries that payload.
- AC:LAttack complexity, low
- check_leaf_item() had no BTRFS_ROOT_REF_KEY/BTRFS_ROOT_BACKREF_KEY case, so btrfs_check_leaf() accepted a ROOT_BACKREF whose item_size filled the leaf (~BTRFS_LEAF_DATA_SIZE). _btrfs_ioctl_get_subvol_info() then copied item_size-sizeof(struct btrfs_root_ref) into name[256] on every ioctl; the attacker fully controls that image.
- PR:LPrivileges required, low
- btrfs_ioctl() dispatches BTRFS_IOC_GET_SUBVOL_INFO and BTRFS_IOC_INO_LOOKUP_USER with no capable() check. btrfs_fs_type has no FS_USERNS_MOUNT, so the severe case is an unprivileged session user whose USB/loop btrfs image is mounted by udisks2/polkit, then opens any fd in that subvolume and issues the ioctl.
- UI:NUser interaction, none
- The attacker crafts the ROOT_BACKREF, has that local image mounted, and themselves calls BTRFS_IOC_GET_SUBVOL_INFO (or BTRFS_IOC_INO_LOOKUP_USER, which copies the same item via btrfs_search_path_in_tree_user()) on their own fd. Automount of that local/removable image is not a separate victim action once AV is Local.
- S:UScope, unchanged
- The overflow is in the host kernel's kzalloc'd btrfs_ioctl_get_subvol_info_args (and ino_lookup_user args) while parsing tree_root ROOT_BACKREF/ROOT_REF items. No KVM/Xen guest-to-host, IOMMU, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- _btrfs_ioctl_get_subvol_info() and btrfs_search_path_in_tree_user() call read_extent_buffer() with a length taken from the on-disk item_size into name[BTRFS_VOL_NAME_MAX+1] (256 bytes). That out-of-bounds write of attacker-chosen leaf bytes into adjacent slab is a kernel-memory disclosure primitive.
- I:HIntegrity impact, high
- The same unbounded read_extent_buffer() into the 256-byte name[] of the kzalloc'd ioctl args overwrites neighboring heap objects with attacker-controlled ROOT_BACKREF payload, which is sufficient for an arbitrary kernel write and control-flow hijacking.
- A:HAvailability impact, high
- Copying a leaf-sized ROOT_BACKREF past btrfs_ioctl_get_subvol_info_args.name[256], or writing args->name[item_len]='\0' in btrfs_search_path_in_tree_user() with that huge item_len, oopses or panics the kernel on the slab out-of-bounds access.