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CVE-2025-6434

Status: ModifiedMedium (4.3)—

The exception page for the HTTPS-Only feature, displayed when a website is opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an attacker to trick a user into granting an exception and loading a webpage over HTTP. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

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-2025-6434",
  "cveTags": [],
  "metrics": {
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          "role": "CISA Coordinator",
          "options": [
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              "exploitation": "none"
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              "automatable": "no"
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              "technicalImpact": "partial"
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          "version": "2.0.3",
          "timestamp": "2025-06-25T14:20:21.535910Z"
        }
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    "cvssMetricV31": [
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          "confidentialityImpact": "NONE"
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  "published": "2025-06-24T13:15:24.447",
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      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1955182",
      "tags": [
        "Permissions Required"
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      "source": "security@mozilla.org"
    },
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      "url": "https://www.mozilla.org/security/advisories/mfsa2025-51/",
      "tags": [
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      "source": "security@mozilla.org"
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      "url": "https://www.mozilla.org/security/advisories/mfsa2025-54/",
      "source": "security@mozilla.org"
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      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "description": [
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          "value": "CWE-1021"
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      "lang": "en",
      "value": "The exception page for the HTTPS-Only feature, displayed when a website is opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an attacker to trick a user into granting an exception and loading a webpage over HTTP. This vulnerability was fixed in Firefox 140 and Thunderbird 140."
    },
    {
      "lang": "es",
      "value": "La página de excepción de la función Solo HTTPS, que se mostraba al abrir un sitio web mediante HTTP, carecía de un retardo anti-clickjacking, lo que potencialmente permitía a un atacante engañar al usuario para que concediera una excepción y cargara una página web mediante HTTP. Esta vulnerabilidad afecta a Firefox anterior a la versión 140."
    }
  ],
  "lastModified": "2026-09-30T18:10:00.190",
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