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CVE-2018-5121

Status: ModifiedMedium (5.3)—

Low descenders on some Tibetan characters in several fonts on OS X are clipped when rendered in the addressbar. When used as part of an Internationalized Domain Name (IDN) this can be used for domain name spoofing attacks. Note: This attack only affects OS X operating systems. Other operating systems are unaffected. This vulnerability affects Firefox < 58.

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-2018-5121",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:L/Au:N/C:N/I:P/A:N",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "LOW",
          "availabilityImpact": "NONE",
          "confidentialityImpact": "NONE"
        },
        "acInsufInfo": false,
        "impactScore": 2.9,
        "baseSeverity": "MEDIUM",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 10,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": false
      }
    ],
    "cvssMetricV30": [
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        "type": "Primary",
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          "scope": "UNCHANGED",
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          "baseScore": 5.3,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 3.9
      }
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  "affected": [
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      "source": "security@mozilla.org",
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          "vendor": "Mozilla",
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              "version": "unspecified",
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              "versionType": "custom"
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  ],
  "published": "2018-06-11T21:29:13.717",
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      "url": "http://www.securityfocus.com/bid/102786",
      "tags": [
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        "VDB Entry"
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      "source": "security@mozilla.org"
    },
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      "source": "security@mozilla.org"
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      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1402368",
      "tags": [
        "Issue Tracking",
        "Permissions Required"
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      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2018-02/",
      "tags": [
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      "source": "security@mozilla.org"
    },
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      "url": "http://www.securityfocus.com/bid/102786",
      "tags": [
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        "VDB Entry"
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
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      "url": "https://www.mozilla.org/security/advisories/mfsa2018-02/",
      "tags": [
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  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Low descenders on some Tibetan characters in several fonts on OS X are clipped when rendered in the addressbar. When used as part of an Internationalized Domain Name (IDN) this can be used for domain name spoofing attacks. Note: This attack only affects OS X operating systems. Other operating systems are unaffected. This vulnerability affects Firefox < 58."
    },
    {
      "lang": "es",
      "value": "Las astas descendentes de algunos caracteres tibetanos en varias fuentes en OS X se recortan cuando se muestran en la barra de direcciones. Cuando se utilizan como parte de un IDN (nombre de dominio internacionalizado), se puede utilizar para realizar ataques de suplantación de nombres de dominio. Nota: este ataque solo afecta a sistemas operativos OS X. Los otros sistemas operativos no se ven afectados. Esta vulnerabilidad afecta a las versiones anteriores a la 58 de Firefox."
    }
  ],
  "lastModified": "2026-06-17T01:59:39.560",
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    {
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  "sourceIdentifier": "security@mozilla.org"
}