CVE-2026-74483 (GCVE-0-2026-74483)

Vulnerability from cvelistv5 – Published: 2026-08-15 12:27 – Updated: 2026-08-23 12:47
VLAI
Title
binfmt_misc: don't leak the user namespace when the mount fails
Summary
In the Linux kernel, the following vulnerability has been resolved: binfmt_misc: don't leak the user namespace when the mount fails bm_get_tree() takes a reference to the user namespace and hands it to get_tree_keyed() as the sget key. sget_fc() moves that reference into sb->s_fs_info and clears fc->s_fs_info, so from that point on the superblock owns it and bm_free() doesn't see it anymore. The superblock drops it in ->put_super(). But generic_shutdown_super() only calls ->put_super() from inside the if (sb->s_root) branch, so nothing releases it when bm_fill_super() fails: - The kzalloc_obj() failure leaves s_root NULL and the whole branch is skipped. - A simple_fill_super() failure in the file loop leaves s_root set, but s_op still points at simple_super_operations, which has no ->put_super(). bm_fill_super() installs s_ops only once simple_fill_super() returned success, and installing it earlier wouldn't help either because simple_fill_super() overwrites s_op. Either way vfs_get_super() calls deactivate_locked_super() and the reference is gone for good. binfmt_misc mounts are available in a user namespace and both the inode and the dentry cache are SLAB_ACCOUNT, so an unprivileged caller under a tight memory cgroup can fail simple_fill_super() on demand and leak one user namespace per attempt. Drop the reference in ->kill_sb() instead, which runs unconditionally, the same way nfsd and rpc_pipefs release their keyed s_fs_info. That also stops ->put_super() from clearing s_fs_info while the superblock is still on @fs_supers. generic_shutdown_super() leaves it there on purpose so that sget_fc() keeps finding it until kill_sb() has run, but a NULL s_fs_info makes test_keyed_super() miss it, so a concurrent mount for the same user namespace skips the grab_super() wait and creates a second superblock for a namespace that is still being torn down.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6856 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 21ca59b365c091d583f36ac753eaa8baf947be6f , < ffec017158d3aad8a6ffca1dfad63d63bde9caad (git)
Affected: 21ca59b365c091d583f36ac753eaa8baf947be6f , < 867aed6a4848761190d5ebdedf9642648f97bceb (git)
Affected: 21ca59b365c091d583f36ac753eaa8baf947be6f , < 87a4eb9bbb3497f749bbac612af22ddaa62d7b0d (git)
Affected: 21ca59b365c091d583f36ac753eaa8baf947be6f , < b8206f516fe7cbe785cf44bf09c17c438d7c3cad (git)
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Linux Linux Affected: 6.7
Unaffected: 0 , < 6.7 (semver)
Unaffected: 6.12.105 , ≤ 6.12.* (semver)
Unaffected: 6.18.46 , ≤ 6.18.* (semver)
Unaffected: 7.1.8 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/binfmt_misc.c"
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          "vendor": "Linux",
          "versions": [
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              "version": "6.7"
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              "version": "0",
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              "versionType": "semver"
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                  "versionStartIncluding": "6.7",
                  "vulnerable": true
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbinfmt_misc: don\u0027t leak the user namespace when the mount fails\n\nbm_get_tree() takes a reference to the user namespace and hands it to\nget_tree_keyed() as the sget key. sget_fc() moves that reference into\nsb-\u003es_fs_info and clears fc-\u003es_fs_info, so from that point on the\nsuperblock owns it and bm_free() doesn\u0027t see it anymore.\n\nThe superblock drops it in -\u003eput_super(). But generic_shutdown_super()\nonly calls -\u003eput_super() from inside the if (sb-\u003es_root) branch, so\nnothing releases it when bm_fill_super() fails:\n\n- The kzalloc_obj() failure leaves s_root NULL and the whole branch is\n  skipped.\n\n- A simple_fill_super() failure in the file loop leaves s_root set, but\n  s_op still points at simple_super_operations, which has no\n  -\u003eput_super(). bm_fill_super() installs s_ops only once\n  simple_fill_super() returned success, and installing it earlier\n  wouldn\u0027t help either because simple_fill_super() overwrites s_op.\n\nEither way vfs_get_super() calls deactivate_locked_super() and the\nreference is gone for good. binfmt_misc mounts are available in a user\nnamespace and both the inode and the dentry cache are SLAB_ACCOUNT, so\nan unprivileged caller under a tight memory cgroup can fail\nsimple_fill_super() on demand and leak one user namespace per attempt.\n\nDrop the reference in -\u003ekill_sb() instead, which runs unconditionally,\nthe same way nfsd and rpc_pipefs release their keyed s_fs_info.\n\nThat also stops -\u003eput_super() from clearing s_fs_info while the\nsuperblock is still on @fs_supers. generic_shutdown_super() leaves it\nthere on purpose so that sget_fc() keeps finding it until kill_sb() has\nrun, but a NULL s_fs_info makes test_keyed_super() miss it, so a\nconcurrent mount for the same user namespace skips the grab_super()\nwait and creates a second superblock for a namespace that is still\nbeing torn down."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-23T12:47:24.496Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/ffec017158d3aad8a6ffca1dfad63d63bde9caad"
        },
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          "url": "https://git.kernel.org/stable/c/867aed6a4848761190d5ebdedf9642648f97bceb"
        },
        {
          "url": "https://git.kernel.org/stable/c/87a4eb9bbb3497f749bbac612af22ddaa62d7b0d"
        },
        {
          "url": "https://git.kernel.org/stable/c/b8206f516fe7cbe785cf44bf09c17c438d7c3cad"
        }
      ],
      "title": "binfmt_misc: don\u0027t leak the user namespace when the mount fails",
      "x_generator": {
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      }
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74483",
    "datePublished": "2026-08-15T12:27:15.709Z",
    "dateReserved": "2026-08-15T05:44:03.904Z",
    "dateUpdated": "2026-08-23T12:47:24.496Z",
    "state": "PUBLISHED"
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      "date": "2026-10-21",
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                "product": "Linux",
                "programFiles": [
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                ],
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                    "versionType": "semver"
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                    "versionType": "semver"
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbinfmt_misc: don\u0027t leak the user namespace when the mount fails\n\nbm_get_tree() takes a reference to the user namespace and hands it to\nget_tree_keyed() as the sget key. sget_fc() moves that reference into\nsb-\u003es_fs_info and clears fc-\u003es_fs_info, so from that point on the\nsuperblock owns it and bm_free() doesn\u0027t see it anymore.\n\nThe superblock drops it in -\u003eput_super(). But generic_shutdown_super()\nonly calls -\u003eput_super() from inside the if (sb-\u003es_root) branch, so\nnothing releases it when bm_fill_super() fails:\n\n- The kzalloc_obj() failure leaves s_root NULL and the whole branch is\n  skipped.\n\n- A simple_fill_super() failure in the file loop leaves s_root set, but\n  s_op still points at simple_super_operations, which has no\n  -\u003eput_super(). bm_fill_super() installs s_ops only once\n  simple_fill_super() returned success, and installing it earlier\n  wouldn\u0027t help either because simple_fill_super() overwrites s_op.\n\nEither way vfs_get_super() calls deactivate_locked_super() and the\nreference is gone for good. binfmt_misc mounts are available in a user\nnamespace and both the inode and the dentry cache are SLAB_ACCOUNT, so\nan unprivileged caller under a tight memory cgroup can fail\nsimple_fill_super() on demand and leak one user namespace per attempt.\n\nDrop the reference in -\u003ekill_sb() instead, which runs unconditionally,\nthe same way nfsd and rpc_pipefs release their keyed s_fs_info.\n\nThat also stops -\u003eput_super() from clearing s_fs_info while the\nsuperblock is still on @fs_supers. generic_shutdown_super() leaves it\nthere on purpose so that sget_fc() keeps finding it until kill_sb() has\nrun, but a NULL s_fs_info makes test_keyed_super() miss it, so a\nconcurrent mount for the same user namespace skips the grab_super()\nwait and creates a second superblock for a namespace that is still\nbeing torn down."
          }
        ],
        "id": "CVE-2026-74483",
        "lastModified": "2026-08-23T13:16:44.530",
        "metrics": {},
        "published": "2026-08-15T13:17:53.163",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/867aed6a4848761190d5ebdedf9642648f97bceb"
          },
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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          }
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
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    },
    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-08-21T08:22:04+00:00",
      "cve": "CVE-2026-74483",
      "id": "CVE-2026-74483",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:known_affected": "90",
      "product_status:known_not_affected": "184",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: binfmt_misc: don\u0027t leak the user namespace when the mount fails",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74483.json",
      "version": "3"
    }
  }
}



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