RHSA-2026:63162
Vulnerability from csaf_redhat - Published: 2026-09-03 12:46 - Updated: 2026-09-06 07:28When an external mount.<type> helper runs but exits with a nonzero status, libmount still treats the helper invocation as successful and runs privileged post-mount hooks. A local unprivileged user with an /etc/fstab entry that uses the user option together with X-mount.idmap or X-mount.owner/group/mode can cause those hooks to clone or re-own the underlying filesystem after the helper fails, leading to local privilege escalation.
| Product | Identifier | Version | Remediation |
|---|---|---|---|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@aarch64 | — |
Vendor Fix
fix
Workaround
|
|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@src | — |
Vendor Fix
fix
Workaround
|
|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@x86_64 | — |
Vendor Fix
fix
Workaround
|
The nsenter --join-cgroup option opens the target cgroup.procs file as root and leaves that file descriptor open across later namespace and credential changes and across execve(). Because the kernel checks later cgroup migrations using the credentials from the original open, a program run in an attacker-controlled target can inherit root's ability to move host processes between cgroups. After a privileged operator uses --join-cgroup against that target, an unprivileged user can migrate and terminate unrelated root processes.
| Product | Identifier | Version | Remediation |
|---|---|---|---|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@aarch64 | — |
Vendor Fix
fix
Workaround
|
|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@src | — |
Vendor Fix
fix
Workaround
|
|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@x86_64 | — |
Vendor Fix
fix
Workaround
|
The X-mount.subdir option uses a detached-tree fast path on Linux 6.15 and later and passes the configured subdirectory to open_tree() with AT_SYMLINK_NOFOLLOW. That flag does not stop intermediate symlink traversal or keep resolution inside the newly mounted filesystem. A local unprivileged user with an fstab-authorized X-mount.subdir entry can attach a host path at the intended mountpoint.
| Product | Identifier | Version | Remediation |
|---|---|---|---|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@aarch64 | — |
Vendor Fix
fix
Workaround
|
|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@src | — |
Vendor Fix
fix
Workaround
|
|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@x86_64 | — |
Vendor Fix
fix
Workaround
|
A flaw was found in util-linux. Restricted bind mounts take the source path from fstab but do not pin that source before the privileged mount. A local unprivileged user who can replace the authorized source or a writable ancestor can redirect SUID mount(8) to bind another host directory. If the fstab entry also sets X-mount.owner, X-mount.group, or X-mount.mode, root then changes ownership or mode on that redirected inode.
| Product | Identifier | Version | Remediation |
|---|---|---|---|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@aarch64 | — |
Vendor Fix
fix
Workaround
|
|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@src | — |
Vendor Fix
fix
Workaround
|
|
| Unresolved product id: Red Hat Hardened Images:util-linux-main@x86_64 | — |
Vendor Fix
fix
Workaround
|
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"notes": [
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"category": "description",
"text": "When an external mount.\u003ctype\u003e helper runs but exits with a nonzero status, libmount still treats the helper invocation as successful and runs privileged post-mount hooks. A local unprivileged user with an /etc/fstab entry that uses the user option together with X-mount.idmap or X-mount.owner/group/mode can cause those hooks to clone or re-own the underlying filesystem after the helper fails, leading to local privilege escalation.",
"title": "Vulnerability description"
},
{
"category": "summary",
"text": "util-linux: util-linux: failed external mount helper still runs privileged X-mount post-hooks",
"title": "Vulnerability summary"
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"date": "2026-09-03T12:46:16+00:00",
"details": "For details on how to apply this update, which includes the changes described in this advisory, refer to:\nhttps://images.redhat.com/",
"product_ids": [
"Red Hat Hardened Images:util-linux-main@aarch64",
"Red Hat Hardened Images:util-linux-main@src",
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"category": "none"
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"url": "https://access.redhat.com/errata/RHSA-2026:63162"
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{
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"details": "Upgrade to util-linux v2.41.6, v2.42.3, or later. Until a fix is applied, avoid combining the user (or users) fstab option with X-mount.idmap or X-mount.owner/group/mode on entries that invoke an external mount.\u003ctype\u003e helper. Administrators can also remove or restrict user-mountable fstab entries that specify those X-mount.* options.",
"product_ids": [
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"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
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"scores": [
{
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"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.8,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"products": [
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"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
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"threats": [
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"category": "impact",
"details": "Important"
}
],
"title": "util-linux: util-linux: failed external mount helper still runs privileged X-mount post-hooks"
},
{
"acknowledgments": [
{
"names": [
"Andreas Gabriel Berbescu"
],
"organization": "Independent Security Researcher"
}
],
"cve": "CVE-2026-78408",
"cwe": {
"id": "CWE-775",
"name": "Missing Release of File Descriptor or Handle after Effective Lifetime"
},
"discovery_date": "2026-07-26T09:22:21+00:00",
"ids": [
{
"system_name": "Red Hat Bugzilla ID",
"text": "2522497"
}
],
"notes": [
{
"category": "description",
"text": "The nsenter --join-cgroup option opens the target cgroup.procs file as root and leaves that file descriptor open across later namespace and credential changes and across execve(). Because the kernel checks later cgroup migrations using the credentials from the original open, a program run in an attacker-controlled target can inherit root\u0027s ability to move host processes between cgroups. After a privileged operator uses --join-cgroup against that target, an unprivileged user can migrate and terminate unrelated root processes.",
"title": "Vulnerability description"
},
{
"category": "summary",
"text": "util-linux: util-linux: nsenter --join-cgroup leaks root cgroup migration authority",
"title": "Vulnerability summary"
},
{
"category": "other",
"text": "Affected versions: util-linux v2.40 through v2.42.2. The --join-cgroup option was introduced in v2.40; earlier releases (including util-linux 2.38) are not affected. Fixed in v2.41.6 and v2.42.3.",
"title": "Statement"
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{
"category": "general",
"text": "The CVSS score(s) listed for this vulnerability do not reflect the associated product\u0027s status, and are included for informational purposes to better understand the severity of this vulnerability.",
"title": "CVSS score applicability"
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"product_ids": [
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"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.9,
"baseSeverity": "HIGH",
"confidentialityImpact": "NONE",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "CHANGED",
"userInteraction": "REQUIRED",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:N/I:H/A:H",
"version": "3.1"
},
"products": [
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"Red Hat Hardened Images:util-linux-main@x86_64"
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],
"threats": [
{
"category": "impact",
"details": "Important"
}
],
"title": "util-linux: util-linux: nsenter --join-cgroup leaks root cgroup migration authority"
},
{
"acknowledgments": [
{
"names": [
"Zhuorao Yang"
],
"organization": "Huawei Cloud",
"summary": "Acknowledged by upstream."
}
],
"cve": "CVE-2026-78409",
"cwe": {
"id": "CWE-59",
"name": "Improper Link Resolution Before File Access (\u0027Link Following\u0027)"
},
"discovery_date": "2026-06-17T00:00:00+00:00",
"ids": [
{
"system_name": "Red Hat Bugzilla ID",
"text": "2522607"
}
],
"notes": [
{
"category": "description",
"text": "The X-mount.subdir option uses a detached-tree fast path on Linux 6.15 and later and passes the configured subdirectory to open_tree() with AT_SYMLINK_NOFOLLOW. That flag does not stop intermediate symlink traversal or keep resolution inside the newly mounted filesystem. A local unprivileged user with an fstab-authorized X-mount.subdir entry can attach a host path at the intended mountpoint.",
"title": "Vulnerability description"
},
{
"category": "summary",
"text": "util-linux: util-linux: X-mount.subdir detached-tree resolution can escape via intermediate symlinks",
"title": "Vulnerability summary"
},
{
"category": "other",
"text": "Affected versions: util-linux v2.42 through v2.42.2. The Linux \u003e= 6.15 detached-tree X-mount.subdir fast path was introduced in ae19f7546ccb (2025-04-15) and first released in v2.42. Earlier releases, including v2.40 and v2.41, are not affected. Restricted-user SUID mount(8) reproduction also requires Linux \u003e= 6.15. Fixed in v2.41.6 and v2.42.3.",
"title": "Statement"
},
{
"category": "general",
"text": "The CVSS score(s) listed for this vulnerability do not reflect the associated product\u0027s status, and are included for informational purposes to better understand the severity of this vulnerability.",
"title": "CVSS score applicability"
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{
"category": "self",
"summary": "Canonical URL",
"url": "https://access.redhat.com/security/cve/CVE-2026-78409"
},
{
"category": "external",
"summary": "RHBZ#2522607",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2522607"
},
{
"category": "external",
"summary": "https://www.cve.org/CVERecord?id=CVE-2026-78409",
"url": "https://www.cve.org/CVERecord?id=CVE-2026-78409"
},
{
"category": "external",
"summary": "https://nvd.nist.gov/vuln/detail/CVE-2026-78409",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78409"
},
{
"category": "external",
"summary": "https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv",
"url": "https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv"
}
],
"release_date": "2026-09-02T00:00:00+00:00",
"remediations": [
{
"category": "vendor_fix",
"date": "2026-09-03T12:46:16+00:00",
"details": "For details on how to apply this update, which includes the changes described in this advisory, refer to:\nhttps://images.redhat.com/",
"product_ids": [
"Red Hat Hardened Images:util-linux-main@aarch64",
"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
],
"restart_required": {
"category": "none"
},
"url": "https://access.redhat.com/errata/RHSA-2026:63162"
},
{
"category": "workaround",
"details": "Upgrade to util-linux v2.41.6, v2.42.3, or later. Until a fix is applied, do not allow unprivileged /etc/fstab entries that specify X-mount.subdir.",
"product_ids": [
"Red Hat Hardened Images:util-linux-main@aarch64",
"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
]
}
],
"scores": [
{
"cvss_v3": {
"attackComplexity": "HIGH",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.0,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"products": [
"Red Hat Hardened Images:util-linux-main@aarch64",
"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
]
}
],
"threats": [
{
"category": "impact",
"details": "Important"
}
],
"title": "util-linux: util-linux: X-mount.subdir detached-tree resolution can escape via intermediate symlinks"
},
{
"acknowledgments": [
{
"names": [
"Zhuorao Yang"
],
"organization": "Huawei Cloud",
"summary": "Acknowledged by upstream."
}
],
"cve": "CVE-2026-78410",
"cwe": {
"id": "CWE-367",
"name": "Time-of-check Time-of-use (TOCTOU) Race Condition"
},
"discovery_date": "2026-06-18T00:00:00+00:00",
"ids": [
{
"system_name": "Red Hat Bugzilla ID",
"text": "2522684"
}
],
"notes": [
{
"category": "description",
"text": "A flaw was found in util-linux. Restricted bind mounts take the source path from fstab but do not pin that source before the privileged mount. A local unprivileged user who can replace the authorized source or a writable ancestor can redirect SUID mount(8) to bind another host directory. If the fstab entry also sets X-mount.owner, X-mount.group, or X-mount.mode, root then changes ownership or mode on that redirected inode.",
"title": "Vulnerability description"
},
{
"category": "summary",
"text": "util-linux: util-linux: restricted bind mounts do not pin the source, allowing X-mount.owner/group/mode redirection",
"title": "Vulnerability summary"
},
{
"category": "other",
"text": "Affected versions: util-linux v2.39 through v2.42.2. X-mount.owner/group/mode was introduced in v2.39; earlier releases are not affected. Fixed in v2.41.6 and v2.42.3.",
"title": "Statement"
},
{
"category": "general",
"text": "The CVSS score(s) listed for this vulnerability do not reflect the associated product\u0027s status, and are included for informational purposes to better understand the severity of this vulnerability.",
"title": "CVSS score applicability"
}
],
"product_status": {
"fixed": [
"Red Hat Hardened Images:util-linux-main@aarch64",
"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
]
},
"references": [
{
"category": "self",
"summary": "Canonical URL",
"url": "https://access.redhat.com/security/cve/CVE-2026-78410"
},
{
"category": "external",
"summary": "RHBZ#2522684",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2522684"
},
{
"category": "external",
"summary": "https://www.cve.org/CVERecord?id=CVE-2026-78410",
"url": "https://www.cve.org/CVERecord?id=CVE-2026-78410"
},
{
"category": "external",
"summary": "https://nvd.nist.gov/vuln/detail/CVE-2026-78410",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78410"
},
{
"category": "external",
"summary": "https://github.com/util-linux/util-linux/security/advisories/GHSA-rh77-686x-2f2m",
"url": "https://github.com/util-linux/util-linux/security/advisories/GHSA-rh77-686x-2f2m"
}
],
"release_date": "2026-09-02T00:00:00+00:00",
"remediations": [
{
"category": "vendor_fix",
"date": "2026-09-03T12:46:16+00:00",
"details": "For details on how to apply this update, which includes the changes described in this advisory, refer to:\nhttps://images.redhat.com/",
"product_ids": [
"Red Hat Hardened Images:util-linux-main@aarch64",
"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
],
"restart_required": {
"category": "none"
},
"url": "https://access.redhat.com/errata/RHSA-2026:63162"
},
{
"category": "workaround",
"details": "Upgrade to util-linux v2.41.6, v2.42.3, or later. Until a fix is applied, do not allow unprivileged /etc/fstab bind or rbind entries that also specify X-mount.owner, X-mount.group, or X-mount.mode, especially when the bind source is below a user-writable ancestor.",
"product_ids": [
"Red Hat Hardened Images:util-linux-main@aarch64",
"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
]
}
],
"scores": [
{
"cvss_v3": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.8,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"products": [
"Red Hat Hardened Images:util-linux-main@aarch64",
"Red Hat Hardened Images:util-linux-main@src",
"Red Hat Hardened Images:util-linux-main@x86_64"
]
}
],
"threats": [
{
"category": "impact",
"details": "Important"
}
],
"title": "util-linux: util-linux: restricted bind mounts do not pin the source, allowing X-mount.owner/group/mode redirection"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.