CVE-2026-46107 dm-thin: fix metadata refcount underflow
A refcount underflow in the Linux kernel's dm-thin module can cause errors and potential denial of service when shared btree nodes are rebalanced.
- 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-2026-46107?
CVE-2026-46107 is a high-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:
dm-thin: fix metadata refcount underflow
There's a bug in dm-thin in the function rebalance_children. If the internal btree node has one entry, the code tries to copy all btree entries from the node's child to the node itself and then decrement the child's reference count.
If the child node is shared (it has reference count > 1), we won't free it, so there would be two pointers to each of the grandchildren nodes. But the reference counts of the grandchildren is not increased, thus the reference count doesn't match the number of pointers that point to the grandchildren. This results in "device mapper: space map common: unable to decrement block" errors.
Fix this bug by incrementing reference counts on the grandchildren if the btree node is shared.
Which versions are affected by CVE-2026-46107?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-46107?
Apply the vendor's patch.
Is CVE-2026-46107 being exploited?
There is no known exploitation of CVE-2026-46107 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-89061, BELL-CVE-2026-46107, DEBIAN-CVE-2026-46107, GHSA-c6hr-v224-3w2w, ROOT-OS-DEBIAN-11-CVE-2026-46107, ROOT-OS-DEBIAN-12-CVE-2026-46107 and 3 more.