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Fencer Vulns
medium 4.7

CVE-2026-27456 json

util-linux: TOCTOU Race Condition in util-linux mount(8) - Loop Device Setup

published 2026-04-03 7 mo ago modified 2026-07-25 3 mo ago also EUVD-2026-18864 , JLSEC-2026-212

cvss
4.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 4%
public exploits
0
none known

Summary

util-linux is a random collection of Linux utilities. Prior to version 2.41.4, a TOCTOU (Time-of-Check-Time-of-Use) vulnerability has been identified in the SUID binary /usr/bin/mount from util-linux. The mount binary, when setting up loop devices, validates the source file path with user privileges via fork() + setuid() + realpath(), but subsequently re-canonicalizes and opens it with root privileges (euid=0) without verifying that the path has not been replaced between both operations. Neither O_NOFOLLOW, nor inode comparison, nor post-open fstat() are employed. This allows a local unprivileged user to replace the source file with a symlink pointing to any root-owned file or device during the race window, causing the SUID binary to open and mount it as root. Exploitation requires an /etc/fstab entry with user,loop options whose path points to a directory where the attacker has write permission, and that /usr/bin/mount has the SUID bit set (the default configuration on virtually all Linux distributions). The impact is unauthorized read access to root-protected files and block devices, including backup images, disk volumes, and any file containing a valid filesystem. This issue has been patched in version 2.41.4.

Patch / fix

  • julia Libmount_jll 2.42.0+0
  • julia Libuuid_jll 2.42.0+0
  • julia util_linux_jll 2.42.0+0
  • kernel util-linux 2.41.4
  • util-linux Debian 13 2.41.5-0+deb13u1
  • util-linux Debian 14 2.42-1

debian advisories DEBIAN-CVE-2026-27456

  • util-linux Ubuntu 22.04 LTS 2.37.2-4ubuntu3.6
  • util-linux Ubuntu 24.04 LTS 2.39.3-9ubuntu6.6
  • util-linux Ubuntu 26.04 LTS 2.41.3-3ubuntu2.2

ubuntu advisories UBUNTU-CVE-2026-27456

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

  • util-linux hummingbird 1 2.42-7.1.hum1
  • util-linux-core hummingbird 1 2.42-7.1.hum1
  • util-linux-i18n hummingbird 1 2.42-7.1.hum1
  • util-linux-script hummingbird 1 2.42-7.1.hum1

red hat advisories RHSA-2026:7180

  • util-linux SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 2.41.1-160000.5.1
  • python-libmount SLES 16.0, SLES for SAP applications 16.0 2.41.1-160000.5.1
  • util-linux-systemd SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 2.41.1-160000.5.1
  • util-linux SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 2.37.4-150500.9.32.1
  • util-linux-systemd SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 2.37.4-150500.9.32.1
  • util-linux SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE Micro 5.4 +3 more 2.37.2-150400.8.50.1
  • util-linux-systemd SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE Micro 5.4 +3 more 2.37.2-150400.8.50.1
  • util-linux Linux Micro 6.1 2.40.4-slfo.1.1_7.1

suse advisories SUSE-SU-2026:4296-1SUSE-SU-2026:23861-1SUSE-SU-2026:23870-1SUSE-SU-2026:23884-1SUSE-SU-2026:3813-1SUSE-SU-2026:3812-1

  • util-linux openSUSE Leap 16.0 2.41.1-160000.5.1
  • python-libmount openSUSE Leap 16.0 2.41.1-160000.5.1
  • util-linux-systemd openSUSE Leap 16.0 2.41.1-160000.5.1
  • util-linux openSUSE Leap 16.0 2.41.1-160000.4.1
  • python-libmount openSUSE Leap 16.0 2.41.1-160000.4.1
  • util-linux-systemd openSUSE Leap 16.0 2.41.1-160000.4.1
  • util-linux openSUSE Tumbleweed 2.42-1.1

opensuse advisories openSUSE-SU-2026:21905-1openSUSE-SU-2026:21028-1openSUSE-SU-2026:10736-1

  • util-linux AlmaLinux 10 2.40.2-18.el10_2.20
  • uuidd AlmaLinux 10 2.40.2-18.el10_2.20
  • libuuid AlmaLinux 10 2.40.2-18.el10_2.20
  • libblkid AlmaLinux 10 2.40.2-18.el10_2.20
  • libfdisk AlmaLinux 10 2.40.2-18.el10_2.20
  • libmount AlmaLinux 10 2.40.2-18.el10_2.20
  • libsmartcols AlmaLinux 10 2.40.2-18.el10_2.20
  • util-linux-core AlmaLinux 10 2.40.2-18.el10_2.20

almalinux advisories ALSA-2026:93461

  • util-linux Rocky Linux 10 2.40.2-18.el10_2.20

rocky linux advisories RLSA-2026:93461

  • util-linux Alpine 3.22 2.41.6-r0
  • util-linux Alpine 3.24, Alpine 3.23 2.41.4-r0
  • util-linux Alpine 3.24 2.42.3-r0

alpine advisories ALPINE-CVE-2026-27456

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • util-linux Azure Linux 3.0 2.40.2-4

azure linux advisories AZL-81846

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

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-2026-27456 updated cvss 4.7

util-linux: TOCTOU in the mount program when setting up loop devices

  • Red Hat Enterprise Linux 8 uuidd, libuuid, libblkid, libfdisk, libmount, util-linux, +3 more Red Hat Enterprise Linux 9 uuidd, libuuid, libblkid, libfdisk, libmount, util-linux, +4 more Red Hat OpenShift Container Platform 4 rhcos
    affected: workaround, no fix available “Fix deferred”
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-core-bff-rhel9, rhoai/odh-dashboard-rhel9, rhoai/odh-mod-arch-maas-rhel9, rhoai/odh-mod-arch-automl-rhel9, rhoai/odh-mod-arch-gen-ai-rhel9, rhoai/odh-mod-arch-mlflow-rhel9, +6 more
    under investigation
  • Red Hat Cost Management On-Premise 1 costmanagement/costmanagement-ui-rhel10 1793825318
    fixed: vendor fix RHSA-2026:95365
  • Red Hat Enterprise Linux AppStream (v. 10) uuidd 2.40.2-18.el10_2.20, python3-libmount 2.40.2-18.el10_2.20 Red Hat Enterprise Linux BaseOS (v. 10) libuuid 2.40.2-18.el10_2.20, libblkid 2.40.2-18.el10_2.20, libfdisk 2.40.2-18.el10_2.20, libmount 2.40.2-18.el10_2.20, util-linux 2.40.2-18.el10_2.20, libsmartcols 2.40.2-18.el10_2.20, +1 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libfdisk-devel 2.40.2-18.el10_2.20, uuidd-debuginfo 2.40.2-18.el10_2.20, libuuid-debuginfo 2.40.2-18.el10_2.20, libblkid-debuginfo 2.40.2-18.el10_2.20, libfdisk-debuginfo 2.40.2-18.el10_2.20, libmount-debuginfo 2.40.2-18.el10_2.20, +6 more
    fixed: vendor fix RHSA-2026:93461
  • Red Hat Hardened Images util-linux 2.42-7.1.hum1, util-linux-core 2.42-7.1.hum1, util-linux-i18n 2.42-7.1.hum1, util-linux-script 2.42-7.1.hum1
    fixed: vendor fix RHSA-2026:7180
  • Red Hat Enterprise Linux 6 uuidd, libuuid, libblkid, util-linux-ng Red Hat Enterprise Linux 7 uuidd, libuuid, libblkid, libmount, util-linux Red Hat Hardened Images uuidd 2.42-7.1.hum1, libuuid 2.42-7.1.hum1, libblkid 2.42-7.1.hum1, libfdisk 2.42-7.1.hum1, libmount 2.42-7.1.hum1, liblastlog2 2.42-7.1.hum1, +2 more Red Hat OpenShift AI (RHOAI) rhoai/odh-mlflow-rhel9, rhoai/odh-kube-rbac-proxy-rhel9, rhoai/odh-maas-controller-rhel9, rhoai/odh-mlflow-operator-rhel9, rhoai/odh-model-controller-rhel9, rhoai/odh-ogx-k8s-operator-rhel9, +14 more
    not affected: vulnerable code not present

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
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.16% chance of exploitation in the next 30 days, higher than 4% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/util-linux/util-linux/security/advisories/GHSA-qq4x-vfq4-9h9g referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
OSV 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
julia Libmount_jll
<2.42.0+0
2.42.0+0
julia Libuuid_jll
<2.42.0+0
2.42.0+0
julia util_linux_jll
<2.42.0+0
2.42.0+0

Affected products

  • util-linux util-linux

Classification

Weakness
  • CWE-59 Improper Link Resolution Before File Access
  • CWE-269 Improper Privilege Management
  • CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

References

Sources

Fencer Vulns 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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.