{
  "crds_version": "0.1",
  "kind": "base",
  "id": "crds:cve-2021-22555",
  "revision": 1,
  "title": "Linux kernel — netfilter heap write to privilege escalation",
  "summary": "A heap write outside its bounds in the Linux kernel's packet filtering tables, present since 2.6.19, lets a local user in a user namespace corrupt memory and take root — or simply bring the machine down.",
  "source_type": "cve",
  "severity": "high",
  "cvss": {
    "score": 7.8,
    "vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
    "version": "3.1"
  },
  "epss": 0.78684,
  "exploitation": {
    "known_exploited": true,
    "exploit_available": true,
    "attack_complexity": "low",
    "kev_added": "2025-10-06",
    "prerequisites": "Local code execution with the ability to create a user namespace."
  },
  "remediation": {
    "patch_available": true
  },
  "mitre_attack": [
    "T1068"
  ],
  "kill_chain": "privilege_escalation",
  "recommended_action": "Patch the kernel to a build carrying the netfilter fix now; where unprivileged user namespaces are not needed, stop allowing them.",
  "confidence": "high",
  "provenance": [
    {
      "fields": [
        "cvss",
        "exploitation.attack_complexity",
        "exploitation.exploit_available",
        "references",
        "published_at"
      ],
      "source": "https://nvd.nist.gov/vuln/detail/CVE-2021-22555",
      "retrieved_at": "2026-09-24T08:51:39.744Z",
      "confidence": "high",
      "extractor": "scrty-crds-pipeline/0.1"
    },
    {
      "fields": [
        "exploitation.known_exploited",
        "exploitation.kev_added"
      ],
      "source": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog",
      "retrieved_at": "2026-09-24T08:51:39.744Z",
      "confidence": "high",
      "extractor": "scrty-crds-pipeline/0.1"
    },
    {
      "fields": [
        "epss"
      ],
      "source": "https://api.first.org/data/v1/epss?cve=CVE-2021-22555",
      "retrieved_at": "2026-09-24T08:51:39.744Z",
      "confidence": "high",
      "extractor": "scrty-crds-pipeline/0.1"
    },
    {
      "fields": [
        "title",
        "summary",
        "severity",
        "remediation",
        "mitre_attack",
        "kill_chain",
        "recommended_action",
        "confidence",
        "tags",
        "exploitation.prerequisites"
      ],
      "source": "https://nvd.nist.gov/vuln/detail/CVE-2021-22555",
      "retrieved_at": "2026-09-24T08:51:39.744Z",
      "confidence": "high",
      "extractor": "claude-code"
    }
  ],
  "references": [
    {
      "type": "cve",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-22555",
      "label": "NVD record"
    },
    {
      "type": "cisa",
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog",
      "label": "CISA Known Exploited Vulnerabilities catalog"
    },
    {
      "type": "vendor_advisory",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492cdc160cd27ce1046cb36f47d3b2b1efa21"
    },
    {
      "type": "vendor_advisory",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457a6511435960115c0f548c4360d5f4801d"
    },
    {
      "type": "exploit",
      "url": "http://packetstormsecurity.com/files/163878/Kernel-Live-Patch-Security-Notice-LSN-0080-1.html"
    }
  ],
  "published_at": "2021-07-07T12:15:08.453Z",
  "issued_at": "2026-09-24T08:51:39.744Z",
  "tags": [
    "linux",
    "kernel",
    "netfilter",
    "privilege-escalation",
    "kev"
  ]
}