ubuntu-cve-2026-72693
Vulnerability from osv_ubuntu
Published
2026-08-13 00:00
Modified
2026-08-13 00:00
Summary
Details

openvt -u is intended to identify the owner of the current VT and then execute login as that user from a privileged context. In the documented kbrequest/init usage, the ownership test in authenticate_user() relies on stat("/proc/<pid>/fd/0"). stat() on /proc/<pid>/fd/0 follows the symlink to the underlying TTY device node. As a result, buf.st_uid reflects the owner of the TTY node rather than the owner of the process holding the file descriptor. If the TTY owner returns to root or the getty owner after logout while an unprivileged process still has fd 0 attached to that TTY, the check can incorrectly treat that process as belonging to the privileged console owner. Once that check succeeds, the -u path executes a passwordless login as the selected user. In the documented kbrequest/init deployment using openvt -us, this can result in passwordless login -f root on the spawned VT. This report establishes that privilege escalation path for that documented deployment; it does not claim equivalent reachability for deployments that do not use openvt -u from a privileged kbrequest/init path.

Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
N/A (UNKNOWN)
medium
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "kbd",
            "binary_version": "1.15.5-1ubuntu1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:14.04:LTS",
        "name": "kbd",
        "purl": "pkg:deb/ubuntu/kbd@1.15.5-1ubuntu1?arch=source\u0026distro=trusty"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.15.5-1ubuntu1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "kbd",
            "binary_version": "1.15.5-1ubuntu5"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:16.04:LTS",
        "name": "kbd",
        "purl": "pkg:deb/ubuntu/kbd@1.15.5-1ubuntu5?arch=source\u0026distro=xenial"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.15.5-1ubuntu4",
        "1.15.5-1ubuntu5"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "kbd",
            "binary_version": "2.0.4-2ubuntu1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:18.04:LTS",
        "name": "kbd",
        "purl": "pkg:deb/ubuntu/kbd@2.0.4-2ubuntu1?arch=source\u0026distro=bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.0.3-2ubuntu3",
        "2.0.4-2ubuntu1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "kbd",
            "binary_version": "2.0.4-4ubuntu2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:20.04:LTS",
        "name": "kbd",
        "purl": "pkg:deb/ubuntu/kbd@2.0.4-4ubuntu2?arch=source\u0026distro=focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.0.4-4ubuntu2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "kbd",
            "binary_version": "2.3.0-3ubuntu4.22.04"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:22.04:LTS",
        "name": "kbd",
        "purl": "pkg:deb/ubuntu/kbd@2.3.0-3ubuntu4.22.04?arch=source\u0026distro=jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.3.0-3ubuntu3",
        "2.3.0-3ubuntu4",
        "2.3.0-3ubuntu4.22.04"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "kbd",
            "binary_version": "2.6.4-2ubuntu2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:24.04:LTS",
        "name": "kbd",
        "purl": "pkg:deb/ubuntu/kbd@2.6.4-2ubuntu2?arch=source\u0026distro=noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.5.1-1ubuntu1",
        "2.6.4-2ubuntu1",
        "2.6.4-2ubuntu2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "kbd",
            "binary_version": "2.7.1-2ubuntu2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:26.04:LTS",
        "name": "kbd",
        "purl": "pkg:deb/ubuntu/kbd@2.7.1-2ubuntu2?arch=source\u0026distro=resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.7.1-2ubuntu1",
        "2.7.1-2ubuntu2"
      ]
    }
  ],
  "aliases": [],
  "details": "`openvt -u` is intended to identify the owner of the current VT and then execute `login` as that user from a privileged context. In the documented `kbrequest`/init usage, the ownership test in `authenticate_user()` relies on `stat(\"/proc/\u003cpid\u003e/fd/0\")`. `stat()` on `/proc/\u003cpid\u003e/fd/0` follows the symlink to the underlying TTY device node. As a result, `buf.st_uid` reflects the owner of the TTY node rather than the owner of the process holding the file descriptor. If the TTY owner returns to `root` or the getty owner after logout while an unprivileged process still has `fd 0` attached to that TTY, the check can incorrectly treat that process as belonging to the privileged console owner. Once that check succeeds, the `-u` path executes a passwordless login as the selected user. In the documented `kbrequest`/init deployment using `openvt -us`, this can result in passwordless `login -f root` on the spawned VT. This report establishes that privilege escalation path for that documented deployment; it does not claim equivalent reachability for deployments that do not use `openvt -u` from a privileged `kbrequest`/init path.",
  "id": "UBUNTU-CVE-2026-72693",
  "modified": "2026-08-13T00:00:00Z",
  "published": "2026-08-13T00:00:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-72693"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-72693"
    },
    {
      "type": "REPORT",
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2462115"
    },
    {
      "type": "REPORT",
      "url": "https://access.redhat.com/security/cve/CVE-2026-72693"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-72693"
  ]
}



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