CVE-2026-43187 xfs: delete attr leaf freemap entries when empty
An integer underflow in the XFS filesystem can cause data loss by allowing extended attribute entries to overwrite existing data.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43187?
CVE-2026-43187 is a high-severity vulnerability in Linux kernel, published on 6 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
xfs: delete attr leaf freemap entries when empty
Back in commit 2a2b5932db6758 ("xfs: fix attr leaf header freemap.size underflow"), Brian Foster observed that it's possible for a small freemap at the end of the end of the xattr entries array to experience a size underflow when subtracting the space consumed by an expansion of the entries array. There are only three freemap entries, which means that it is not a complete index of all free space in the leaf block.
This code can leave behind a zero-length freemap entry with a nonzero base. Subsequent setxattr operations can increase the base up to the point that it overlaps with another freemap entry. This isn't in and of itself a problem because the code in _leaf_add that finds free space ignores any freemap entry with zero size.
However, there's another bug in the freemap update code in _leaf_add, which is that it fails to update a freemap entry that begins midway through the xattr entry that was just appended to the array. That can result in the freemap containing two entries with the same base but different sizes (0 for the "pushed-up" entry, nonzero for the entry that's actually tracking free space). A subsequent _leaf_add can then allocate xattr namevalue entries on top of the entries array, leading to data loss. But fixing that is for later.
For now, eliminate the possibility of confusion by zeroing out the base of any freemap entry that has zero size. Because the freemap is not intended to be a complete index of free space, a subsequent failure to find any free space for a new xattr will trigger block compaction, which regenerates the freemap.
It looks like this bug has been in the codebase for quite a long time.
Which versions are affected by CVE-2026-43187?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43187?
Apply the vendor's patch.
Is CVE-2026-43187 being exploited?
There is no known exploitation of CVE-2026-43187 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43187, DEBIAN-CVE-2026-43187, GHSA-8h5h-g93f-3ff6, ROOT-OS-DEBIAN-11-CVE-2026-43187, ROOT-OS-UBUNTU-2204-CVE-2026-43187, ROOT-OS-UBUNTU-2404-CVE-2026-43187 and 1 more.