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CVE-2020-26959

Estado: ModificadaAlta (8.8)—

During browser shutdown, reference decrementing could have occured on a previously freed object, resulting in a use-after-free, memory corruption, and a potentially exploitable crash. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (3)

Mozilla — FirefoxMozilla — Firefox ESRMozilla — Thunderbird

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2020-26959",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 6.8,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "MEDIUM",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "PARTIAL"
        },
        "acInsufInfo": false,
        "impactScore": 6.4,
        "baseSeverity": "MEDIUM",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 8.6,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": true
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 8.8,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "REQUIRED",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 2.8
      }
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  "affected": [
    {
      "source": "security@mozilla.org",
      "affectedData": [
        {
          "vendor": "Mozilla",
          "product": "Firefox",
          "versions": [
            {
              "status": "affected",
              "version": "< 83"
            }
          ]
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        {
          "vendor": "Mozilla",
          "product": "Firefox ESR",
          "versions": [
            {
              "status": "affected",
              "version": "< 78.5"
            }
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          "vendor": "Mozilla",
          "product": "Thunderbird",
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              "version": "< 78.5"
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  "published": "2020-12-09T01:15:13.143",
  "references": [
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      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1669466",
      "tags": [
        "Issue Tracking",
        "Permissions Required",
        "Vendor Advisory"
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      "source": "security@mozilla.org"
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      "tags": [
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      "url": "https://www.mozilla.org/security/advisories/mfsa2020-51/",
      "tags": [
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      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2020-52/",
      "tags": [
        "Vendor Advisory"
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      "source": "security@mozilla.org"
    },
    {
      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1669466",
      "tags": [
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        "Vendor Advisory"
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
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    {
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      "tags": [
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    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2020-51/",
      "tags": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2020-52/",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-416"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "During browser shutdown, reference decrementing could have occured on a previously freed object, resulting in a use-after-free, memory corruption, and a potentially exploitable crash. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5."
    },
    {
      "lang": "es",
      "value": "Durante el cierre del navegador, la disminución de la referencia podría haber ocurrido en un objeto previamente liberado, resultando en un uso de la memoria previamente liberada, una corrupción de la memoria y un bloqueo potencialmente explotable. Esta vulnerabilidad afecta a Firefox versiones anteriores a 83, Firefox ESR versiones anteriores a 78.5, y Thunderbird versiones anteriores a 78.5"
    }
  ],
  "lastModified": "2026-06-17T03:08:37.300",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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              "vulnerable": true,
              "matchCriteriaId": "9385C808-43DD-4D02-B1A9-89A2E3986DF2",
              "versionEndExcluding": "83.0"
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              "versionEndExcluding": "78.5"
            },
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  "sourceIdentifier": "security@mozilla.org"
}