kbd — security advisory
`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//fd/0")`. `stat()` on `/proc//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.
- Products
- kbd
- Affected versions
- 1.15.5-1ubuntu1, 1.15.5-1ubuntu4, 1.15.5-1ubuntu5, 2.0.3-2ubuntu3, 2.0.4-2ubuntu1, 2.0.4-4ubuntu2, 2.3.0-3ubuntu3, 2.3.0-3ubuntu4, 2.3.0-3ubuntu4.22.04, 2.5.1-1ubuntu1, 2.6.4-2ubuntu1, 2.6.4-2ubuntu2, 2.7.1-2ubuntu1, 2.7.1-2ubuntu2, 2.9.0-1ubuntu1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-72693
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 03:15 UTC · Revision 1
Source evidence
`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//fd/0")`. `stat()` on `/proc//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.
osv:UBUNTU-CVE-2026-72693
kbd
Fixed versions: Not specified
kbd
Fixed versions: Not specified
kbd
Fixed versions: Not specified
kbd
Fixed versions: Not specified
kbd
Fixed versions: Not specified
kbd
Fixed versions: Not specified
kbd
Fixed versions: Not specified
kbd
Fixed versions: Not specified
Complete source record
{
"id": "ea792f727951edd419f5a70375926d400ac8cb77ff8d5b5a64de0ce251269bcc",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-72693",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-72693",
"summary": "`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//fd/0\")`. `stat()` on `/proc//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.",
"evidence": "osv:UBUNTU-CVE-2026-72693",
"products": [
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],
"severity": "high",
"structured": {
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"aliases": [
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"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
},
{
"type": "Ubuntu",
"score": "medium"
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"affected": [
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"versions": [
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"database_specific": {
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},
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"ecosystem": "Ubuntu:16.04:LTS"
},
"versions": [
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"1.15.5-1ubuntu5"
],
"database_specific": {
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},
"versions": [
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],
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},
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],
"modified": "2026-10-17T13:00:49.046003556Z",
"provider": "osv",
"upstream": [
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],
"references": [
"https://ubuntu.com/security/CVE-2026-72693",
"https://www.cve.org/CVERecord?id=CVE-2026-72693",
"https://access.redhat.com/security/cve/CVE-2026-72693"
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"source_id": "core-osv",
"document_id": 360850,
"published_at": "2026-08-11T09:17:00+00:00"
}