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CVE-2026-63818
f2fs: validate orphan inode entry count
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs/f2fs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-63818 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 | fixedDSA-6393-1 · 2026-07-21 · text | 6.12.96-1 | Update the kernel and reboot. DSA-6393-1 shipped the fix on 2026-07-21, in 6.12.96-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. 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
f2fs_recover_orphan_inodes() trusts the orphan block entry_count when replaying orphan inodes from the checkpoint pack. A corrupted entry_count larger than F2FS_ORPHANS_PER_BLOCK makes the recovery loop read past the ino[] array and interpret footer or following data as inode numbers. On a crafted image, mounting an unpatched kernel can drive orphan recovery into f2fs_bug_on() and panic the kernel. Validate entry_count before consuming entries so corrupted checkpoint data fails the mount with -EFSCORRUPTED and requests fsck instead. Set ERROR_INCONSISTENT_ORPHAN as well, so the corruption reason can be recorded in the superblock s_errors[] field. This gives fsck a persistent hint even though mount-time orphan recovery failure may leave no chance to persist SBI_NEED_FSCK through a checkpoint.
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/f2fs/checkpoint.c
include/linux/f2fs_fs.h
- What this is
- F2FS FILE SYSTEMMAINTAINERS section matched on fs/f2fs/ · linux-f2fs-devel@lists.sourceforge.net · Maintained
- Kernel module
- f2fs
Check it on the machine
grep -w CONFIG_F2FS_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 f2fsPrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookworm, trixie, forky, sid, bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_F2FS_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
- 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
- not yet assignedsource
- Subsystem
- fs/f2fs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 3.8 | 5.10.261 | 210c210c92d7 |
| 3.8 | 5.15.212 | ad101d15716f |
| 3.8 | 6.1.178 | d18c81f5d0ec |
| 3.8 | 6.6.145 | d2f236196d54 |
| 3.8 | 6.12.96 | 550511a2470f |
| 3.8 | 6.18.38 | 8aad54746c25 |
| 3.8 | 7.1.3 | 2e12381d4495 |
| 3.8 | 7.2 | 846c499a6581 |
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 |
| DSA-6393-1 | 2026-07-21 | trixie 6.12.96-1 | 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 vulnerable code runs only during F2FS mount via the mount syscall path (fs_context → get_tree_bdev → f2fs_fill_super → f2fs_recover_orphan_inodes); it is not reachable from network protocols or device drivers.
- AC:LAttack complexity, low
- An attacker fully controls the crafted on-disk orphan block including entry_count and ino[] contents, so triggering the bug is reliable once a victim or privileged auto-mount path mounts the image; no race or rare layout dependency is required.
- PR:NPrivileges required, none
- The attacker needs no privileges on the victim system—only a malicious F2FS image delivered via removable media, downloaded disk image, or similar that a privileged mount/auto-mount daemon later processes.
- UI:NUser interaction, none
- No victim interaction is required when the attacker mounts their own crafted image (e.g., loop mount in a user namespace with CAP_SYS_ADMIN), and automated privileged mount paths can process attacker-supplied media without further user action.
- S:UScope, unchanged
- Impact is confined to kernel/filesystem integrity and availability on the host mounting the image; it does not cross a VM, container, or IOMMU security boundary.
- C:HConfidentiality impact, high
- The unchecked loop indexes past ino[F2FS_ORPHANS_PER_BLOCK-1] into the block footer and beyond the 4 KiB orphan block, constituting an out-of-bounds read of attacker-influenced metadata that can leak kernel-adjacent memory contents.
- I:HIntegrity impact, high
- Misinterpreted inode numbers are passed to recover_orphan_inode(), which clear_nlink() and iput() (truncating data) on matching real inodes, enabling deliberate destruction of filesystem contents from a crafted image.
- A:HAvailability impact, high
- Crafted entry_count values drive f2fs_bug_on() on -ENOENT (kernel BUG/panic with CONFIG_F2FS_CHECK_FS, or WARN/oops otherwise) and can hang or crash the system during mount via unbounded orphan recovery iteration.