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CVE-2021-43533

Status: ModifiedMedium (4.3)—

When parsing internationalized domain names, high bits of the characters in the URLs were sometimes stripped, resulting in inconsistencies that could lead to user confusion or attacks such as phishing. This vulnerability affects Firefox < 94.

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)

Show
{
  "id": "CVE-2021-43533",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
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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,
        "obtainUserPrivilege": false,
        "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:U/C:N/I:L/A:N",
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          "userInteraction": "REQUIRED",
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          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
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        "exploitabilityScore": 2.8
      }
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  "affected": [
    {
      "source": "security@mozilla.org",
      "affectedData": [
        {
          "vendor": "Mozilla",
          "product": "Firefox",
          "versions": [
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              "status": "affected",
              "version": "unspecified",
              "lessThan": "94",
              "versionType": "custom"
            }
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  ],
  "published": "2021-12-08T22:15:09.420",
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      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1724233",
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        "Vendor Advisory"
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      "tags": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
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      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
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          "lang": "en",
          "value": "NVD-CWE-noinfo"
        }
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  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "When parsing internationalized domain names, high bits of the characters in the URLs were sometimes stripped, resulting in inconsistencies that could lead to user confusion or attacks such as phishing. This vulnerability affects Firefox < 94."
    },
    {
      "lang": "es",
      "value": "Cuando eran analizados los nombres de dominio internacionalizados, a veces se eliminaban los bits altos de los caracteres de las URL, resultando en incoherencias que podían conllevar a una confusión para el usuario o ataques como el phishing. Esta vulnerabilidad afecta a Firefox versiones anteriores a 94"
    }
  ],
  "lastModified": "2026-06-17T04:11:04.960",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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              "versionEndExcluding": "94.0"
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          "operator": "OR"
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  "sourceIdentifier": "security@mozilla.org"
}