binfmt_misc: don't warn when the mount is completed from another user namespace

{
  "id": "17fa79a89c3ddb84ccf2220e03aa8be09dfd5ac06ef0fea5d3a9609c5acbec39",
  "url": "https://osv.dev/vulnerability/CVE-2026-74618",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "binfmt_misc: don't warn when the mount is completed from another user namespace",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: binfmt_misc: 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 bm_fill_super(): create a user and a mount namespace in a child, call fsopen(\"binfmt_misc\") 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/binfmt_misc.c:938 at bm_fill_super+0xa2/0xc0 [binfmt_misc] CPU: 15 UID: 1000 PID: 3243382 Comm: fswarn Call Trace: get_tree_keyed+0x7d/0xb0 bm_get_tree+0x34/0x90 [binfmt_misc] 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 re",
    "evidence": "osv:CVE-2026-74618",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.104",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.45",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.1.9",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-74618",
      "aliases": [
        "CVE-2026-74618"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "21ca59b365c091d583f36ac753eaa8baf947be6f"
                },
                {
                  "fixed": "37cf5cf1320a84a17225a1690547b8a0812ca94e"
                },
                {
                  "fixed": "24e95a24f151ce40d5fc1b3a6cefbcda8ded736c"
                },
                {
                  "fixed": "047f927f54c6c17593e93aafe82dcb7acdda2a71"
                },
                {
                  "fixed": "79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74618.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.104"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.45"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.1.9"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74618.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:40.031659892Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/047f927f54c6c17593e93aafe82dcb7acdda2a71",
        "https://git.kernel.org/stable/c/24e95a24f151ce40d5fc1b3a6cefbcda8ded736c",
        "https://git.kernel.org/stable/c/37cf5cf1320a84a17225a1690547b8a0812ca94e",
        "https://git.kernel.org/stable/c/79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74618.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-74618",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74618.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-74618",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 507358,
  "published_at": "2026-08-22T15:32:02.778+00:00"
}