{
  "crds_version": "0.1",
  "kind": "base",
  "id": "crds:cve-2021-27137",
  "revision": 1,
  "title": "DD-WRT — UPnP stack buffer overflow RCE",
  "summary": "The DD-WRT router firmware (DD-WRT builds before 45724) copies data unsafely in its Universal Plug and Play (UPnP) service. An unauthenticated attacker in reach sends a crafted discovery (M-SEARCH) request to overflow a buffer and run code on the router. UPnP is off by default.",
  "source_type": "cve",
  "severity": "high",
  "cvss": {
    "score": 8.1,
    "vector": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
    "version": "3.1"
  },
  "epss": 0.03995,
  "exploitation": {
    "known_exploited": true,
    "exploit_available": true,
    "attack_complexity": "high",
    "kev_added": "2026-07-21",
    "prerequisites": "Network reach to the router's UPnP (SSDP) listener; UPnP must be enabled by the user (off by default and internal-interface only by default)."
  },
  "remediation": {
    "patch_available": true,
    "workaround_available": true,
    "fixed_in": [
      "DD-WRT 45724"
    ]
  },
  "mitre_attack": [
    "T1190"
  ],
  "kill_chain": "initial_access",
  "recommended_action": "Update DD-WRT to build 45724 or later; until then disable UPnP on affected routers and check for C0xmo/Gafgyt botnet activity.",
  "confidence": "high",
  "provenance": [
    {
      "fields": [
        "cvss",
        "exploitation.attack_complexity",
        "exploitation.exploit_available",
        "references",
        "published_at"
      ],
      "source": "https://nvd.nist.gov/vuln/detail/CVE-2021-27137",
      "retrieved_at": "2026-09-22T06:10:25.213Z",
      "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": "2026-09-22T06:10:25.213Z",
      "confidence": "high",
      "extractor": "scrty-crds-pipeline/0.1"
    },
    {
      "fields": [
        "epss"
      ],
      "source": "https://api.first.org/data/v1/epss?cve=CVE-2021-27137",
      "retrieved_at": "2026-09-22T06:10:25.213Z",
      "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-2021-27137",
      "retrieved_at": "2026-09-22T06:10:25.213Z",
      "confidence": "high",
      "extractor": "claude-code"
    }
  ],
  "references": [
    {
      "type": "cve",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-27137",
      "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://svn.dd-wrt.com/changeset/45724"
    },
    {
      "type": "exploit",
      "url": "https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html"
    },
    {
      "type": "exploit",
      "url": "https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/"
    }
  ],
  "published_at": "2026-07-16T18:16:39.113Z",
  "issued_at": "2026-09-22T06:10:25.213Z",
  "tags": [
    "dd-wrt",
    "upnp",
    "buffer-overflow",
    "router",
    "kev",
    "botnet"
  ]
}