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CVE-2025-6429

Status: ModifiedMedium (6.5)—

Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an `embed` tag. This could have bypassed website security checks that restricted which domains users were allowed to embed. This vulnerability was fixed in Firefox 140, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

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-2025-6429",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2025-6429",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2025-06-25T14:21:21.354270Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.5,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N",
          "integrityImpact": "HIGH",
          "userInteraction": "REQUIRED",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 2.8
      }
    ]
  },
  "affected": [
    {
      "source": "security@mozilla.org",
      "affectedData": [
        {
          "vendor": "Mozilla",
          "product": "Firefox",
          "versions": [
            {
              "status": "unaffected",
              "version": "128.12",
              "versionType": "rpm",
              "lessThanOrEqual": "128.*"
            },
            {
              "status": "unaffected",
              "version": "140",
              "versionType": "rpm",
              "lessThanOrEqual": "*"
            }
          ]
        },
        {
          "vendor": "Mozilla",
          "product": "Thunderbird",
          "versions": [
            {
              "status": "unaffected",
              "version": "128.12",
              "versionType": "rpm",
              "lessThanOrEqual": "128.*"
            },
            {
              "status": "unaffected",
              "version": "140",
              "versionType": "rpm",
              "lessThanOrEqual": "*"
            }
          ]
        }
      ]
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  ],
  "published": "2025-06-24T13:15:23.877",
  "references": [
    {
      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1970658",
      "tags": [
        "Permissions Required"
      ],
      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2025-51/",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2025-53/",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2025-54/",
      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2025-55/",
      "source": "security@mozilla.org"
    },
    {
      "url": "https://lists.debian.org/debian-lts-announce/2025/06/msg00029.html",
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://lists.debian.org/debian-lts-announce/2025/07/msg00002.html",
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "description": [
        {
          "lang": "en",
          "value": "CWE-116"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an `embed` tag.  This could have bypassed website security checks that restricted which domains users were allowed to embed. This vulnerability was fixed in Firefox 140, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12."
    },
    {
      "lang": "es",
      "value": "Firefox podría haber analizado incorrectamente una URL y reescrito el dominio youtube.com al analizar la URL especificada en una etiqueta 'embed'. Esto podría haber eludido las comprobaciones de seguridad del sitio web que restringían los dominios que los usuarios podían incrustar. Esta vulnerabilidad afecta a Firefox con versiones anteriores a 140 y Firefox con ESR inferior a 128.12."
    }
  ],
  "lastModified": "2026-09-30T18:10:00.190",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "18420C6D-A5DF-41A4-8A81-F1BBFBA1BE2A",
              "versionEndExcluding": "128.12.0"
            },
            {
              "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "77D2BF2A-26A3-4664-93B5-B41BCF17AC9E",
              "versionEndExcluding": "140.0"
            }
          ],
          "operator": "OR"
        }
      ]
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  ],
  "sourceIdentifier": "security@mozilla.org"
}