{
  "cvss": 8.9,
  "datePublished": "2025-12-05T16:15:51.053",
  "dateUpdated": "2026-09-25T23:10:00.463",
  "description": "urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.",
  "id": "CVE-2025-66418",
  "raw": {
    "affected": [
      {
        "affectedData": [
          {
            "product": "urllib3",
            "vendor": "urllib3",
            "versions": [
              {
                "status": "affected",
                "version": ">= 1.24, < 2.6.0"
              }
            ]
          }
        ],
        "source": "security-advisories@github.com"
      }
    ],
    "configurations": [
      {
        "nodes": [
          {
            "cpeMatch": [
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                "criteria": "cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:*",
                "matchCriteriaId": "AE1F753E-4D9D-48B1-B893-B3FD39917478",
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                "versionStartIncluding": "1.24",
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              }
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            "negate": false,
            "operator": "OR"
          }
        ]
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    ],
    "cveTags": [],
    "descriptions": [
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        "lang": "en",
        "value": "urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0."
      },
      {
        "lang": "es",
        "value": "urllib3 es una biblioteca cliente HTTP fácil de usar para Python. A partir de la versión 1.24 y en versiones anteriores a la 2.6.0, el número de enlaces en la cadena de descompresión era ilimitado, lo que permitía a un servidor malicioso insertar un número prácticamente ilimitado de pasos de compresión, lo que provocaba un alto uso de CPU y una asignación masiva de memoria para los datos descomprimidos. Esta vulnerabilidad se corrigió en la versión 2.6.0."
      }
    ],
    "id": "CVE-2025-66418",
    "lastModified": "2026-09-25T23:10:00.463",
    "metrics": {
      "cvssMetricV31": [
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
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            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
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            "Recovery": "NOT_DEFINED",
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            "confidentialityRequirement": "NOT_DEFINED",
            "exploitMaturity": "NOT_DEFINED",
            "integrityRequirement": "NOT_DEFINED",
            "modifiedAttackComplexity": "NOT_DEFINED",
            "modifiedAttackRequirements": "NOT_DEFINED",
            "modifiedAttackVector": "NOT_DEFINED",
            "modifiedPrivilegesRequired": "NOT_DEFINED",
            "modifiedSubAvailabilityImpact": "NOT_DEFINED",
            "modifiedSubConfidentialityImpact": "NOT_DEFINED",
            "modifiedSubIntegrityImpact": "NOT_DEFINED",
            "modifiedUserInteraction": "NOT_DEFINED",
            "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
            "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
            "modifiedVulnIntegrityImpact": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "HIGH",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
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                "exploitation": "none"
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                "automatable": "yes"
              },
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                "technicalImpact": "partial"
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            "role": "CISA Coordinator",
            "timestamp": "2025-12-05T16:15:39.701596Z",
            "version": "2.0.3"
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    "published": "2025-12-05T16:15:51.053",
    "references": [
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        "source": "security-advisories@github.com",
        "tags": [
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        "url": "https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8"
      },
      {
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        "tags": [
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    "vulnStatus": "Analyzed",
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            "lang": "en",
            "value": "CWE-770"
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        "type": "Secondary"
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  "severity": "HIGH",
  "source": "nvd",
  "title": "urllib3 is a user-friendly HTTP client library for Python"
}