CVE-2026-74619 (GCVE-0-2026-74619)

Vulnerability from cvelistv5 – Published: 2026-08-22 15:32 – Updated: 2026-08-22 15:32
VLAI
Title
ovl: don't warn when the mount is completed from another user namespace
Summary
In the Linux kernel, the following vulnerability has been resolved: ovl: don't warn when the mount is completed from another user namespace fsopen() records the caller's user namespace in fc->user_ns and hands back an ordinary file descriptor. Nothing ties the task that calls fsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The fd is inherited across fork() and exec() and it can be passed over a unix socket. Completing a context from another user namespace is allowed on purpose. vfs_cmd_create() authorizes the create with mount_capable(), which for FS_USERNS_MOUNT checks ns_capable(fc->user_ns, CAP_SYS_ADMIN), and that succeeds for a task holding CAP_SYS_ADMIN in an ancestor of fc->user_ns. So an unprivileged task can reach the WARN_ON() in ovl_fill_super(): create a user and a mount namespace in a child, call fsopen("overlay") there, send the fscontext fd to the parent and let the parent issue FSCONFIG_CMD_CREATE. Both namespaces come from a plain unshare(1) and no capability is needed anywhere: WARNING: fs/overlayfs/super.c:1551 at ovl_fill_super+0x7b9/0x1e20 [overlay] CPU: 3 UID: 1000 PID: 3243376 Comm: fswarn Call Trace: get_tree_nodev+0x71/0xa0 ovl_get_tree+0x15/0x20 [overlay] vfs_get_tree+0x2a/0x100 vfs_cmd_create+0x60/0xf0 __do_sys_fsconfig+0x4b2/0x500 The child needs the mount namespace because fsopen() itself gates on may_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning the caller's mount namespace. fsconfig() doesn't repeat that check. It is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be raised in a loop to taint the kernel and flood the log, and it panics a kernel booted with panic_on_warn. Keep refusing the mount and stop warning about it. ovl_parse_param() already spells a user namespace check this way for Opt_override_creds.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6665 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1784fbc2ed9c888ea4e895f30a53207ed7ee8208 , < 513478092966dc9818d96dd2b3ed613fd2f6e30e (git)
Affected: 1784fbc2ed9c888ea4e895f30a53207ed7ee8208 , < 494346f2aab2489d379d43ff614aea447cf4e94d (git)
Affected: 1784fbc2ed9c888ea4e895f30a53207ed7ee8208 , < be161fa31e3e9cc828a3c1bd935edca461e8a7a1 (git)
Affected: 1784fbc2ed9c888ea4e895f30a53207ed7ee8208 , < 42d99fcd8006007e2f708bede6789f37f3910b30 (git)
Affected: 1784fbc2ed9c888ea4e895f30a53207ed7ee8208 , < 63981fc786daaa626cb14d9be1406f674d79f98f (git)
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Linux Linux Affected: 6.5
Unaffected: 0 , < 6.5 (semver)
Unaffected: 6.6.152 , ≤ 6.6.* (semver)
Unaffected: 6.12.104 , ≤ 6.12.* (semver)
Unaffected: 6.18.45 , ≤ 6.18.* (semver)
Unaffected: 7.1.9 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\novl: don\u0027t warn when the mount is completed from another user namespace\n\nfsopen() records the caller\u0027s user namespace in fc-\u003euser_ns and hands\nback an ordinary file descriptor. Nothing ties the task that calls\nfsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The\nfd is inherited across fork() and exec() and it can be passed over a\nunix socket.\n\nCompleting a context from another user namespace is allowed on purpose.\nvfs_cmd_create() authorizes the create with mount_capable(), which for\nFS_USERNS_MOUNT checks ns_capable(fc-\u003euser_ns, CAP_SYS_ADMIN), and that\nsucceeds for a task holding CAP_SYS_ADMIN in an ancestor of fc-\u003euser_ns.\nSo an unprivileged task can reach the WARN_ON() in ovl_fill_super():\ncreate a user and a mount namespace in a child, call fsopen(\"overlay\")\nthere, send the fscontext fd to the parent and let the parent issue\nFSCONFIG_CMD_CREATE. Both namespaces come from a plain unshare(1) and no\ncapability is needed anywhere:\n\n  WARNING: fs/overlayfs/super.c:1551 at ovl_fill_super+0x7b9/0x1e20 [overlay]\n  CPU: 3 UID: 1000 PID: 3243376 Comm: fswarn\n  Call Trace:\n   get_tree_nodev+0x71/0xa0\n   ovl_get_tree+0x15/0x20 [overlay]\n   vfs_get_tree+0x2a/0x100\n   vfs_cmd_create+0x60/0xf0\n   __do_sys_fsconfig+0x4b2/0x500\n\nThe child needs the mount namespace because fsopen() itself gates on\nmay_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning\nthe caller\u0027s mount namespace. fsconfig() doesn\u0027t repeat that check.\n\nIt is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be\nraised in a loop to taint the kernel and flood the log, and it panics a\nkernel booted with panic_on_warn.\n\nKeep refusing the mount and stop warning about it. ovl_parse_param()\nalready spells a user namespace check this way for Opt_override_creds."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-22T15:32:03.511Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/513478092966dc9818d96dd2b3ed613fd2f6e30e"
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          "url": "https://git.kernel.org/stable/c/494346f2aab2489d379d43ff614aea447cf4e94d"
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      "title": "ovl: don\u0027t warn when the mount is completed from another user namespace",
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    "cveId": "CVE-2026-74619",
    "datePublished": "2026-08-22T15:32:03.511Z",
    "dateReserved": "2026-08-15T05:44:03.921Z",
    "dateUpdated": "2026-08-22T15:32:03.511Z",
    "state": "PUBLISHED"
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      "percentile": "0.05665"
    },
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      "current_release_date": "2026-09-25T01:55:22.000Z",
      "cve": "CVE-2026-74619",
      "id": "msrc_CVE-2026-74619",
      "initial_release_date": "2026-08-24T01:04:15.000Z",
      "product_status:fixed": "1",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "ovl: don\u0027t warn when the mount is completed from another user namespace",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-74619.json",
      "version": "4"
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                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
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                "versions": [
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                    "version": "6.5"
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                    "status": "unaffected",
                    "version": "0",
                    "versionType": "semver"
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                    "status": "unaffected",
                    "version": "6.6.152",
                    "versionType": "semver"
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                  {
                    "lessThanOrEqual": "6.12.*",
                    "status": "unaffected",
                    "version": "6.12.104",
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                  {
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                    "status": "unaffected",
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\novl: don\u0027t warn when the mount is completed from another user namespace\n\nfsopen() records the caller\u0027s user namespace in fc-\u003euser_ns and hands\nback an ordinary file descriptor. Nothing ties the task that calls\nfsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The\nfd is inherited across fork() and exec() and it can be passed over a\nunix socket.\n\nCompleting a context from another user namespace is allowed on purpose.\nvfs_cmd_create() authorizes the create with mount_capable(), which for\nFS_USERNS_MOUNT checks ns_capable(fc-\u003euser_ns, CAP_SYS_ADMIN), and that\nsucceeds for a task holding CAP_SYS_ADMIN in an ancestor of fc-\u003euser_ns.\nSo an unprivileged task can reach the WARN_ON() in ovl_fill_super():\ncreate a user and a mount namespace in a child, call fsopen(\"overlay\")\nthere, send the fscontext fd to the parent and let the parent issue\nFSCONFIG_CMD_CREATE. Both namespaces come from a plain unshare(1) and no\ncapability is needed anywhere:\n\n  WARNING: fs/overlayfs/super.c:1551 at ovl_fill_super+0x7b9/0x1e20 [overlay]\n  CPU: 3 UID: 1000 PID: 3243376 Comm: fswarn\n  Call Trace:\n   get_tree_nodev+0x71/0xa0\n   ovl_get_tree+0x15/0x20 [overlay]\n   vfs_get_tree+0x2a/0x100\n   vfs_cmd_create+0x60/0xf0\n   __do_sys_fsconfig+0x4b2/0x500\n\nThe child needs the mount namespace because fsopen() itself gates on\nmay_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning\nthe caller\u0027s mount namespace. fsconfig() doesn\u0027t repeat that check.\n\nIt is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be\nraised in a loop to taint the kernel and flood the log, and it panics a\nkernel booted with panic_on_warn.\n\nKeep refusing the mount and stop warning about it. ovl_parse_param()\nalready spells a user namespace check this way for Opt_override_creds."
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\novl: no advertir cuando el montaje se completa desde otro espacio de nombres de usuario\n\nfsopen() registra el espacio de nombres de usuario del llamador en fc -\u003e user_ns y devuelve un descriptor de archivo ordinario. Nada vincula la tarea que llama a fsconfig(FSCONFIG_CMD_CREATE) con la tarea que cre\u00f3 el contexto. El fd se hereda a trav\u00e9s de fork() y exec() y puede pasarse a trav\u00e9s de un socket unix.\n\nCompletar un contexto desde otro espacio de nombres de usuario est\u00e1 permitido a prop\u00f3sito. vfs_cmd_create() autoriza la creaci\u00f3n con mount_capable(), que para FS_USERNS_MOUNT comprueba ns_capable(fc -\u003e user_ns, CAP_SYS_ADMIN), y eso tiene \u00e9xito para una tarea que posee CAP_SYS_ADMIN en un ancestro de fc -\u003e user_ns. As\u00ed, una tarea sin privilegios puede alcanzar el WARN_ON() en ovl_fill_super(): crear un espacio de nombres de usuario y de montaje en un hijo, llamar a fsopen(\u0027overlay\u0027) all\u00ed, enviar el fd del fscontext al padre y dejar que el padre emita FSCONFIG_CMD_CREATE. Ambos espacios de nombres provienen de un simple unshare(1) y no se necesita ninguna capacidad en ning\u00fan lugar:\n\n  WARNING: fs/overlayfs/super.c:1551 at ovl_fill_super+0x7b9/0x1e20 [overlay]\n  CPU: 3 UID: 1000 PID: 3243376 Comm: fswarn\n  Call Trace:\n   get_tree_nodev+0x71/0xa0\n   ovl_get_tree+0x15/0x20 [overlay]\n   vfs_get_tree+0x2a/0x100\n   vfs_cmd_create+0x60/0xf0\n   __do_sys_fsconfig+0x4b2/0x500\n\nEl hijo necesita el espacio de nombres de montaje porque fsopen() mismo se basa en may_mount(), que solicita CAP_SYS_ADMIN en el espacio de nombres de usuario propietario del espacio de nombres de montaje del llamador. fsconfig() no repite esa comprobaci\u00f3n.\n\nEs un WARN_ON() y no un WARN_ON_ONCE(), por lo que la condici\u00f3n puede ser elevada en un bucle para corromper el kernel e inundar el registro, y provoca un p\u00e1nico en un kernel arrancado con panic_on_warn.\n\nSeguir rechazando el montaje y dejar de advertir al respecto. ovl_parse_param() ya especifica una comprobaci\u00f3n del espacio de nombres de usuario de esta manera para Opt_override_creds."
          }
        ],
        "id": "CVE-2026-74619",
        "lastModified": "2026-10-14T13:10:00.187",
        "metrics": {},
        "published": "2026-08-22T16:16:34.623",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/42d99fcd8006007e2f708bede6789f37f3910b30"
          },
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/513478092966dc9818d96dd2b3ed613fd2f6e30e"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/63981fc786daaa626cb14d9be1406f674d79f98f"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/be161fa31e3e9cc828a3c1bd935edca461e8a7a1"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-24T14:36:11+00:00",
      "cve": "CVE-2026-74619",
      "id": "CVE-2026-74619",
      "initial_release_date": "2026-08-22T00:00:00+00:00",
      "product_status:known_affected": "184",
      "product_status:known_not_affected": "90",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ovl: don\u0027t warn when the mount is completed from another user namespace",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74619.json",
      "version": "3"
    }
  }
}



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