CVE-2026-72108

What it is

In the Linux kernel, the following vulnerability has been resolved: dm thin metadata: fix metadata snapshot consistency on commit failure __reserve_metadata_snap() and __release_metadata_snap() modify the superblock's held_root directly in the block_manager's buffer. If the subsequent metadata commit fails, the held_root gets flushed to disk through the abort_transaction path, resulting in inconsistent metadata. Reproducer 1: __reserve_metadata_snap() 1. Create a 2 MiB metadata device and make the region after the 14th block inaccessible, to trigger metadata commit failure in the subsequent reserve_metadata_snap operation. The 14th block will be the shadow destination for the index block. dmsetup create tmeta --table "0 112 linear /dev/sdc 0 112 3984 error" 2. Create a 16 MiB thin-pool dmsetup create tdata --table "0 32768 zero" dd if=/dev/zero of=/dev/mapper/tmeta bs=4k count=1 dmsetup create tpool --table "0 32768 thin-pool /dev/mapper/tmeta \ /dev/mapper/tdata 128 0 1 skip_block_zeroing" 3. Take a metadata snapshot to trigger metadata commit failure and transaction abort. However, the held_root is written to disk, breaking metadata consistency. dmsetup message tpool 0 "reserve_metadata_snap" thin_check v1.2.2 result: Bad reference count for metadata block 6. Expected 2, but space map contains 1. Bad reference count for metadata block 7. Expected 2, but space map contains 1. Bad reference count for metadata block 13. Expected 1, but space map contains 0. Reproducer 2: __release_metadata_snap() 1. Create a 2 MiB metadata device and make the region after the 16th block inaccessible, to trigger metadata commit failure in the subsequent release_metadata_snap operation. The 16th block will be the shadow destination for the index block. dmsetup create tmeta --table "0 128 linear /dev/sdc 0 128 3968 error" 2. Create a 16 MiB thin-pool dmsetup create tdata --table "0 32768 zero" dd if=/dev/zero of=/dev/mapper/tmeta bs=4k count=1 dmsetup create tpool --table "0 32768 thin-pool /dev/mapper/tmeta \ /dev/mapper/tdata 128 0 1 skip_block_zeroing" 3. Reserve then release the metadata snapshot, to trigger metadata commit failure and transaction abort. The held_root gets removed from the on-disk superblock, causing inconsistent metadata. dmsetup message tpool 0 "reserve_metadata_snap" dmsetup message tpool 0 "release_metadata_snap" thin_check v1.2.2 result: Bad reference count for metadata block 6. Expected 1, but space map contains 2. Bad reference count for metadata block 7. Expected 1, but space map contains 2. 1 metadata blocks have leaked. Fix by deferring the held_root update to commit time. Additionally, move the existing-snapshot check in __reserve_metadata_snap before the shadow operation to avoid unnecessary work. In __release_metadata_snap, clear pmd->held_root before btree deletion so partial failure leaks blocks rather than leaving a stale reference, and unlock the snapshot block before decrementing its refcount.

At a glance

Exploitability

Can be exploited locally on the machine with a low-privilege account. High risk of data exposure, data tampering, service disruption.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-08-15 06:21 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-19 22:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.3% in the next 30 days (EPSS).
• Severity: 7.8 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-08-15 06:21 UTC

Last modified

2026-10-19 22:17 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-672

Record status

Received

Attack profile CVSS 3.1 · 7.8

Attack vector

Local

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

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Read https://cve-list.com/agent/cve/CVE-2026-72108.md and follow it. Check whether this project is affected by CVE-2026-72108. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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