CVE-2026-78409

Full vulnerability record from the local CVENow database.
Description

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.
Severity
HIGH
CVSS score
7.0 (v3.1)
Vulnerability status
Awaiting Analysis
Source identifier
[email protected]
Published
2026-09-02 16:17:23.833000
Last modified
2026-10-21 18:17:28.967000
View original CVE JSON
{
  "id": "CVE-2026-78409",
  "sourceIdentifier": "[email protected]",
  "published": "2026-09-02T16:17:23.833",
  "lastModified": "2026-10-21T18:17:28.967",
  "vulnStatus": "Awaiting Analysis",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "Red Hat",
          "product": "Red Hat Hardened Images",
          "defaultStatus": "affected",
          "collectionURL": "https://catalog.redhat.com/software/containers/",
          "packageName": "util-linux-main",
          "cpes": [
            "cpe:/a:redhat:hummingbird:1"
          ],
          "versions": [
            {
              "version": "2.42.2-3.4.hum1",
              "lessThan": "*",
              "versionType": "rpm",
              "status": "unaffected"
            }
          ]
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 10",
          "defaultStatus": "unaffected",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "util-linux",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:10"
          ]
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 7",
          "defaultStatus": "unaffected",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "util-linux",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:7"
          ]
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 8",
          "defaultStatus": "unaffected",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "util-linux",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:8"
          ]
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 9",
          "defaultStatus": "unaffected",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "rhel8/flatpak-runtime",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:9"
          ]
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 9",
          "defaultStatus": "unaffected",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "rhel8/flatpak-sdk",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:9"
          ]
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 9",
          "defaultStatus": "unaffected",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "util-linux",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:9"
          ]
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat OpenShift Container Platform 4",
          "defaultStatus": "unaffected",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "openshift/ose-rhel-coreos-8",
          "cpes": [
            "cpe:/a:redhat:openshift:4"
          ]
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat OpenShift Container Platform 4",
          "defaultStatus": "unaffected",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "openshift/ose-rhel-coreos-9",
          "cpes": [
            "cpe:/a:redhat:openshift:4"
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "baseScore": 7.0,
          "baseSeverity": "HIGH",
          "attackVector": "LOCAL",
          "attackComplexity": "HIGH",
          "privilegesRequired": "LOW",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 1.0,
        "impactScore": 5.9
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-09-02T15:29:06.011028Z",
          "id": "CVE-2026-78409",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-59"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://access.redhat.com/errata/RHSA-2026:63162",
      "source": "[email protected]"
    },
    {
      "url": "https://access.redhat.com/security/cve/CVE-2026-78409",
      "source": "[email protected]"
    },
    {
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2522607",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv",
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"
    }
  ]
}