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Fencer Intel
medium 5.5

CVE-2025-38066 json

dm cache: prevent BUG_ON by blocking retries on failed device resumes

published last yr. modified 4d ago also EUVD-2025-18587

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 10%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

dm cache: prevent BUG_ON by blocking retries on failed device resumes

A cache device failing to resume due to mapping errors should not be retried, as the failure leaves a partially initialized policy object. Repeating the resume operation risks triggering BUG_ON when reloading cache mappings into the incomplete policy object.

Reproduce steps:

1. create a cache metadata consisting of 512 or more cache blocks, with some mappings stored in the first array block of the mapping array. Here we use cache_restore v1.0 to build the metadata.

cat <<EOF >> cmeta.xml <superblock uuid="" block_size="128" nr_cache_blocks="512" \ policy="smq" hint_width="4"> <mappings> <mapping cache_block="0" origin_block="0" dirty="false"/> </mappings> </superblock> EOF dmsetup create cmeta --table "0 8192 linear /dev/sdc 0" cache_restore -i cmeta.xml -o /dev/mapper/cmeta --metadata-version=2 dmsetup remove cmeta

2. wipe the second array block of the mapping array to simulate data degradations.

mapping_root=$(dd if=/dev/sdc bs=1c count=8 skip=192 \ 2>/dev/null | hexdump -e '1/8 "%u\n"') ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096*mapping_root+2056)) \ 2>/dev/null | hexdump -e '1/8 "%u\n"') dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$ablock

3. try bringing up the cache device. The resume is expected to fail due to the broken array block.

dmsetup create cmeta --table "0 8192 linear /dev/sdc 0" dmsetup create cdata --table "0 65536 linear /dev/sdc 8192" dmsetup create corig --table "0 524288 linear /dev/sdc 262144" dmsetup create cache --notable dmsetup load cache --table "0 524288 cache /dev/mapper/cmeta \ /dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0" dmsetup resume cache

4. try resuming the cache again. An unexpected BUG_ON is triggered while loading cache mappings.

dmsetup resume cache

Kernel logs:

(snip) ------------[ cut here ]------------ kernel BUG at drivers/md/dm-cache-policy-smq.c:752! Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI CPU: 0 UID: 0 PID: 332 Comm: dmsetup Not tainted 6.13.4 #3 RIP: 0010:smq_load_mapping+0x3e5/0x570

Fix by disallowing resume operations for devices that failed the initial attempt.

Patch / fix

  • Linux Linux 5.4.294, 5.10.238, 5.15.185, 6.1.141, 6.6.93, 6.12.31, 6.14.9, 6.15
  • linux Debian 12 6.1.147-1
  • linux Debian 14, Debian 13 6.12.32-1

debian advisories DEBIAN-CVE-2025-38066

  • linux Ubuntu 22.04 LTS 5.15.0-152.162
  • linux Ubuntu 24.04 LTS 6.8.0-100.100
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1090.97
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1046.49
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1090.99
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1047.50
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1087.93
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1043.48

ubuntu advisories UBUNTU-CVE-2025-38066

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel Azure Linux 3.0 6.6.96.1-1

azure linux advisories AZL-63938

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-38066 updated cvss 4.7

kernel: dm cache: prevent BUG_ON by blocking retries on failed device resumes

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    affected: no fix available

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
4d ago

Exploit prediction

0.21% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.