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CVE-2021-38501

Status: ModifiedHigh (8.8)—

Mozilla developers reported memory safety bugs present in Firefox 92 and Firefox ESR 91.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 93, Thunderbird < 91.2, and Firefox ESR < 91.2.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (3)

Mozilla — FirefoxMozilla — Firefox ESRMozilla — Thunderbird

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-38501",
  "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
      }
    ]
  },
  "affected": [
    {
      "source": "security@mozilla.org",
      "affectedData": [
        {
          "vendor": "Mozilla",
          "product": "Firefox",
          "versions": [
            {
              "status": "affected",
              "version": "unspecified",
              "lessThan": "93",
              "versionType": "custom"
            }
          ]
        },
        {
          "vendor": "Mozilla",
          "product": "Thunderbird",
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              "status": "affected",
              "version": "unspecified",
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            }
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        },
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          "vendor": "Mozilla",
          "product": "Firefox ESR",
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              "version": "unspecified",
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              "versionType": "custom"
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  ],
  "published": "2021-11-03T01:15:07.617",
  "references": [
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      "url": "https://bugzilla.mozilla.org/buglist.cgi?bug_id=1685354%2C1715755%2C1723176",
      "tags": [
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      "source": "security@mozilla.org"
    },
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      "url": "https://www.mozilla.org/security/advisories/mfsa2021-43/",
      "tags": [
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      ],
      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2021-45/",
      "tags": [
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      "source": "security@mozilla.org"
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      "tags": [
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      "source": "security@mozilla.org"
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      "tags": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
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      "tags": [
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "NVD-CWE-noinfo"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Mozilla developers reported memory safety bugs present in Firefox 92 and Firefox ESR 91.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 93, Thunderbird < 91.2, and Firefox ESR < 91.2."
    },
    {
      "lang": "es",
      "value": "Los desarrolladores de Mozilla informaron de bugs de seguridad de memoria presentes en Firefox 92 y Firefox ESR 91.1. Algunos de estos bugs mostraban evidencias de corrupción de memoria y suponemos que con suficiente esfuerzo algunos de ellos podrían haber sido explotados para ejecutar código arbitrario. Esta vulnerabilidad afecta a Firefox versiones anteriores a 93, Thunderbird versiones anteriores a 91.2 y Firefox ESR versiones anteriores a 91.2"
    }
  ],
  "lastModified": "2026-06-17T04:02:14.180",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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              "vulnerable": true,
              "matchCriteriaId": "B38B28B1-FAB5-47DB-9C73-0CFB79CCDE79",
              "versionEndExcluding": "93.0"
            },
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  "sourceIdentifier": "security@mozilla.org"
}