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CVE-2026-90118
ntfs: fix off-by-one page overflow in ntfs_decompress()
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem fs/ntfs. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-90118 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 | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| 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. |
The vulnerability
What the bug is
The per-token range check in ntfs_decompress() uses if (cb >= cb_sb_end || dp_addr > dp_sb_end) break; so dp_addr == dp_sb_end falls through to the symbol copy `*dp_addr++ = *cb++`, writing one byte past the destination page. Since NTFS_SB_SIZE == PAGE_SIZE the destination is a single page, so the byte lands in the adjacent page, and *dest_ofs is left one past the sub-block end (the later `*dest_ofs &= ~PAGE_MASK` then yields 1, not 0, so the page is never finalized and later sub-blocks keep writing further past it). A corrupted compressed $DATA attribute thus produces a bounded run of out-of-bounds writes when the file is read. Break as soon as dp_addr reaches dp_sb_end; a full sub-block still completes, as its final copy advances dp_addr to exactly dp_sb_end.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/ntfs/compress.c
- What this is
- NTFS FILESYSTEMMAINTAINERS section matched on fs/ntfs/ · linux-fsdevel@vger.kernel.org · Maintained
- Kernel module
- ntfs
Check it on the machine
grep -w CONFIG_NTFS_FS /boot/config-$(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 ntfsPrints 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 does not build this code in 1 release. It does build it in 2 releases, so the answer depends on which release the machine runs. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookwormn
- trixie?
- forky, sidm
- n
- not enabled on any flavour - this release does not build the code
- ?
- not established - no Makefile entry for the affected file
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switch
- CONFIG_NTFS_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
- 2026-09-17 (31 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/ntfs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 7.1 | 7.2.6 | b42644e425fe |
| 7.1 | 7.3 | 98716c9fce21 |
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 overflowing bytes are LZNT-style symbol tokens in a compressed unnamed $DATA attribute. They reach ntfs_decompress() only after ntfs_file_read_iter→generic_file_read_iter→ntfs_read_folio→ntfs_read_compressed_block() copies those clusters from the block device; a remote client does not carry the token stream.
- AC:LAttack complexity, low
- A crafted compressed $DATA that leaves dp_addr==dp_sb_end makes the per-token `dp_addr > dp_sb_end` check fall through to `*dp_addr++ = *cb++`. Ending the sub-block so `*dest_ofs &= ~PAGE_MASK` yields 1 is deterministic and does not depend on a race or uninfluenced layout.
- PR:NPrivileges required, none
- The attacker only needs to supply the image that contains the malformed compressed $DATA; ntfs_fs_type has no FS_USERNS_MOUNT so mount_capable() needs init-namespace CAP_SYS_ADMIN, which is the victim's mount (UI:R), not an attacker privilege on the target.
- UI:RUser interaction, required
- The malformed tokens exist only on the attacker-supplied volume. ntfs_get_tree()→get_tree_bdev()→ntfs_fill_super() must mount that image before ntfs_file_read_iter can read the compressed file and enter ntfs_decompress().
- S:UScope, unchanged
- The write past kmap_local_page() of dest_pages[] corrupts the host kernel's adjacent page in the same OS security domain; it is not a VM, IOMMU, or sandbox boundary crossing.
- C:HConfidentiality impact, high
- The off-by-one `*dp_addr++ = *cb++` plus later sub-blocks (dest_ofs left at 1, so the dest folio is never finalized) overwrite the physically adjacent kernel page, a memory-corruption primitive that can be leveraged for kernel information disclosure.
- I:HIntegrity impact, high
- Each overflowing symbol token writes an attacker-chosen byte from the compressed stream one past the destination page, and later sub-blocks keep writing further past it into the adjacent page, an out-of-bounds kernel write usable for control-flow hijack.
- A:HAvailability impact, high
- Writing past the kmap_local_page() mapping of the dest folio into the next pfn can oops or panic the kernel on the ntfs_file_read_iter→ntfs_decompress() path even when the overflow is not turned into a reliable write primitive.