CVE-2026-46107
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk3th percentile - higher than 3% of all known CVEs
Summary
In the Linux kernel's dm-thin module, a bug was found in the rebalance_children function where reference counts for grandchild nodes are not incremented when a shared child node is processed. This leads to metadata refcount underflow and 'unable to decrement block' errors.
Risk Assessment
The bug can cause filesystem instability and data integrity loss on dm-thin volumes. Block allocation errors may lead to metadata corruption and potential data unavailability.
Recommendation
Apply the latest Linux kernel patch containing the dm-thin fix. This update should be prioritized on systems using thin provisioning in Device Mapper.
Original NVD description (English source)
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.