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CVE-2021-23959

Status: ModifiedMedium (6.1)—

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

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 (1)

Mozilla — Firefox

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-23959",
  "cveTags": [],
  "metrics": {
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        "type": "Primary",
        "source": "nvd@nist.gov",
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          "baseScore": 4.3,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:M/Au:N/C:N/I:P/A:N",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "MEDIUM",
          "availabilityImpact": "NONE",
          "confidentialityImpact": "NONE"
        },
        "acInsufInfo": false,
        "impactScore": 2.9,
        "baseSeverity": "MEDIUM",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 8.6,
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        "obtainOtherPrivilege": false,
        "userInteractionRequired": true
      }
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    "cvssMetricV31": [
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          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
          "integrityImpact": "LOW",
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            }
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  "published": "2021-02-26T03:15:13.853",
  "references": [
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      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1659035",
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      "tags": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
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  ],
  "vulnStatus": "Modified",
  "weaknesses": [
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      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
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      ]
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  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85."
    },
    {
      "lang": "es",
      "value": "Un bug de tipo XSS en las páginas de error internas podría conllevar a varios ataques de suplantación de identidad, incluyendo otras páginas de error y la barra de direcciones.&#xa0;Nota: este problema solo afectó a Firefox para Android.&#xa0;Otros sistemas operativos no están afectados.&#xa0;Esta vulnerabilidad afecta a Firefox versiones anteriores a 85"
    }
  ],
  "lastModified": "2026-06-17T03:39:04.253",
  "configurations": [
    {
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              "versionEndExcluding": "85.0"
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  "sourceIdentifier": "security@mozilla.org"
}