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CVE-2026-63954
hpfs: fix a crash if hpfs_map_dnode_bitmap fails
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs/hpfs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-63954 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 | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
If hpfs_map_dnode_bitmap fails, the code would call hpfs_brelse4 on uninitialized quad buffer head, causing a crash.
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/hpfs/alloc.c
- What this is
- HPFS FILESYSTEMMAINTAINERS section matched on fs/hpfs/ · Maintained
- Kernel module
- hpfs
Check it on the machine
grep -w CONFIG_HPFS_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 hpfsPrints 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, sidMnot 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_HPFS_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
- 0.17%, higher than 5.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/hpfs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.12 | 5.10.259 | 010b08084000 |
| 2.6.12 | 5.15.210 | d98d8562b328 |
| 2.6.12 | 6.1.176 | 1648a3c7f4e1 |
| 2.6.12 | 6.6.143 | 7c58c55a2a16 |
| 2.6.12 | 6.12.93 | 1d73a533760b |
| 2.6.12 | 6.18.35 | 0886c6f257fe |
| 2.6.12 | 7.0.12 | 4f37bb30b57d |
| 2.6.12 | 7.1 | 974820a59efd |
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 only through local VFS syscalls (mkdir, create, unlink, rename) on a mounted HPFS filesystem; HPFS is a local block-device filesystem with no network-facing kernel server component.
- AC:LAttack complexity, low
- An attacker can reliably force `hpfs_map_dnode_bitmap()` to fail by mounting a crafted image (e.g. with `check=none` and an invalid `dir_band_bitmap`) or by corrupting the loop/backing device after mount to induce read errors, then triggering a directory operation.
- PR:LPrivileges required, low
- Exploitation requires mounting HPFS (achievable with CAP_SYS_ADMIN inside an unprivileged user namespace) and write access to the mountpoint; it does not require real root in the initial namespace.
- UI:NUser interaction, none
- In the highest-impact path, the attacker mounts their own malicious HPFS image inside a user namespace and triggers the bug themselves without requiring any victim action such as plugging in media or mounting untrusted storage.
- S:UScope, unchanged
- Impact is confined to kernel memory management within the same kernel security domain; there is no crossing of VM, container, or IOMMU boundaries.
- C:HConfidentiality impact, high
- Calling `hpfs_brelse4()` on an uninitialized `quad_buffer_head` performs `kfree()` and `brelse()` on stack garbage, which is uncontrolled memory corruption that can corrupt slab metadata or dereference arbitrary pointers, not a bounded NULL dereference.
- I:HIntegrity impact, high
- The erroneous `kfree()`/`brelse()` calls on uninitialized pointers can corrupt kernel heap state and potentially be leveraged for arbitrary writes, matching the guidance to score uncertain memory-corruption bugs at High.
- A:HAvailability impact, high
- The bug reliably causes a kernel oops or panic when `hpfs_map_dnode_bitmap()` fails, resulting in complete loss of system availability for the affected host.