CVE-2026-90200 fs/ntfs3: fix integer overflow in MFT cluster validation
An integer overflow in the Linux kernel NTFS3 driver allows bypassing validation, leading to mount failures and denial of service when processing malformed boot sectors.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-90200?
CVE-2026-90200 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
In the Linux kernel, the following vulnerability has been resolved:
fs/ntfs3: fix integer overflow in MFT cluster validation
In ntfs_init_from_boot(), the boot sector's MFT cluster numbers are validated against the volume size with:
if (mlcn * sct_per_clst >= sectors || mlcn2 * sct_per_clst >= sectors) goto out;
mlcn and mlcn2 are u64 fields read directly from the boot sector. sct_per_clst is bounded above by 4096 (true_sectors_per_clst() plus the is_power_of_2() check below it), but the multiplication is done in u64 and wraps when mlcn (or mlcn2) is large enough -- e.g. mlcn near 2^62 with sct_per_clst == 4 wraps to 0, which compares below any non-zero 'sectors', so the check is bypassed and the malformed record is accepted.
The accepted mlcn is then used unchanged in
sbi->mft.lbo = mlcn << cluster_bits;
In practice the resulting reads fail at the block layer (sb_bread() returns NULL via grow_buffers()'s check_mul_overflow() guard), so today this manifests as mount failing in odd places rather than as something more dangerous, but the validation step is still wrong and there is no reason for callers to rely on the block layer to catch a value that should never have been accepted in the first place.
Use check_mul_overflow() to compute the two sector positions and fail the mount if either multiplication wraps; this preserves the existing semantics (mlcn * sct_per_clst >= sectors) instead of switching to division (mlcn >= sectors / sct_per_clst), which would tighten the check at edge cases where 'sectors' is not a multiple of sct_per_clst. The check_*_overflow() style is the one ntfs3 already uses for similar on-disk arithmetic in fs/ntfs3/run.c.
Which versions are affected by CVE-2026-90200?
How do I fix CVE-2026-90200?
Apply the vendor's patch.
Is CVE-2026-90200 being exploited?
There is no known exploitation of CVE-2026-90200 in the wild and no public exploit code.
Sources
Also known as AZL-102926, BELL-CVE-2026-90200, DEBIAN-CVE-2026-90200, GHSA-h945-5whj-h8mc, UBUNTU-CVE-2026-90200.