CVE-2026-46159 btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which can lead to info-leak
A race condition in the Linux kernel btrfs filesystem allows local attackers to read uninitialized heap memory via an information leak.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-46159?
CVE-2026-46159 is a medium-severity vulnerability in Linux kernel, published on 28 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which can lead to info-leak
btrfs_ioctl_space_info() has a TOCTOU race between two passes over the block group RAID type lists. The first pass counts entries to determine the allocation size, then the second pass fills the buffer. The groups_sem rwlock is released between passes, allowing concurrent block group removal to reduce the entry count.
When the second pass fills fewer entries than the first pass counted, copy_to_user() copies the full alloc_size bytes including trailing uninitialized kmalloc bytes to userspace.
Fix by copying only total_spaces entries (the actually-filled count from the second pass) instead of alloc_size bytes, and switch to kzalloc so any future copy size mismatch cannot leak heap data.
Weakness: CWE-367
Which versions are affected by CVE-2026-46159?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-46159?
Apply the vendor's patch.
Is CVE-2026-46159 being exploited?
There is no known exploitation of CVE-2026-46159 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-88815, BELL-CVE-2026-46159, DEBIAN-CVE-2026-46159, GHSA-8m37-fqxx-cfwj, ROOT-OS-DEBIAN-11-CVE-2026-46159, ROOT-OS-DEBIAN-12-CVE-2026-46159 and 3 more.