{
  "schemaVersion": 1,
  "attribution": [
    {
      "source": "CISA Known Exploited Vulnerabilities",
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog",
      "licence": "US government work"
    },
    {
      "source": "GitHub Advisory Database",
      "url": "https://github.com/advisories",
      "licence": "CC BY 4.0"
    },
    {
      "source": "Have I Been Pwned",
      "url": "https://haveibeenpwned.com/",
      "licence": "CC BY 4.0"
    },
    {
      "source": "CVE Program (CVE records)",
      "url": "https://www.cve.org/Legal/TermsOfUse",
      "licence": "CVE Terms of Use",
      "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.",
      "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy."
    },
    {
      "source": "FIRST EPSS",
      "url": "https://www.first.org/epss/",
      "licence": "free to use; FIRST requests attribution"
    }
  ],
  "record": {
    "id": "CVE-2021-47555",
    "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2021-47555",
    "idYear": 2021,
    "status": "PUBLISHED",
    "publishedAt": "2024-05-24T15:09:57.302Z",
    "updatedAt": "2026-08-05T08:48:23.118Z",
    "importedAt": "2026-10-24T01:56:36.661Z",
    "snapshot": {
      "id": "cve_2026-10-24_midnight_baseline",
      "at": "2026-10-24T00:00:00.000Z",
      "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z"
    },
    "facts": {
      "title": "net: vlan: fix underflow for the real_dev refcnt",
      "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: vlan: fix underflow for the real_dev refcnt\n\nInject error before dev_hold(real_dev) in register_vlan_dev(),\nand execute the following testcase:\n\nip link add dev dummy1 type dummy\nip link add name dummy1.100 link dummy1 type vlan id 100\nip link del dev dummy1\n\nWhen the dummy netdevice is removed, we will get a WARNING as following:\n\n=======================================================================\nrefcount_t: decrement hit 0; leaking memory.\nWARNING: CPU: 2 PID: 0 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0\n\nand an endless loop of:\n\n=======================================================================\nunregister_netdevice: waiting for dummy1 to become free. Usage count = -1073741824\n\nThat is because dev_put(real_dev) in vlan_dev_free() be called without\ndev_hold(real_dev) in register_vlan_dev(). It makes the refcnt of real_dev\nunderflow.\n\nMove the dev_hold(real_dev) to vlan_dev_init() which is the call-back of\nndo_init(). That makes dev_hold() and dev_put() for vlan's real_dev\nsymmetrical.",
      "affected": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "versions": [
            {
              "version": "700602b662d7eaa816b1a3cb0abe7a85de358fd4",
              "status": "affected",
              "versionType": "git",
              "lessThan": "5e44178864b38dd70b877985abd7d86fdb95f27d"
            },
            {
              "version": "e04a7a84bb77f9cdf4475340fe931389bc72331c",
              "status": "affected",
              "versionType": "git",
              "lessThan": "6e800ee43218a56acc93676bbb3d93b74779e555"
            },
            {
              "version": "21032425c36ff85f16e72ca92193a8c401e4acd5",
              "status": "affected",
              "versionType": "git",
              "lessThan": "f7fc72a508cf115c273a7a29350069def1041890"
            },
            {
              "version": "563bcbae3ba233c275c244bfce2efe12938f5363",
              "status": "affected",
              "versionType": "git",
              "lessThan": "01d9cc2dea3fde3bad6d27f464eff463496e2b00"
            },
            {
              "version": "fca96b3f852a1b369b7b2844ce357cd689879934",
              "status": "affected",
              "versionType": "git"
            },
            {
              "version": "5.14.19",
              "status": "affected",
              "versionType": "semver",
              "lessThan": "5.15"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "versions": [
            {
              "version": "5.4.160",
              "status": "affected",
              "versionType": "semver",
              "lessThan": "5.4.163"
            },
            {
              "version": "5.10.80",
              "status": "affected",
              "versionType": "semver",
              "lessThan": "5.10.83"
            },
            {
              "version": "5.15.3",
              "status": "affected",
              "versionType": "semver",
              "lessThan": "5.15.6"
            }
          ]
        }
      ]
    }
  }
}