How severe is CVE-2025-6433?

CVE-2025-6433 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2025-6433 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-6433?

CVE-2025-6433 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-6433?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2025-6433 have an EU (EUVD) identifier?

Yes. CVE-2025-6433 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-19088.

When was CVE-2025-6433 published?

CVE-2025-6433 was published on 2025-06-24 and last updated on 2026-06-17.

CVE-2025-6433

CVE-2025-6433 is a critical-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-295.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 0% (15th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-19088
Weakness: CWE-295
Affected product: Mozilla Firefox
Published: 2025-06-24
Last modified: 2026-06-17

Description

If a user visited a webpage with an invalid TLS certificate, and granted an exception, the webpage was able to provide a WebAuthn challenge that the user would be prompted to complete. This is in violation of the WebAuthN spec which requires "a secure transport established without errors". This vulnerability was fixed in Firefox 140 and Thunderbird 140.

Frequently asked questions

What is CVE-2025-6433?: If a user visited a webpage with an invalid TLS certificate, and granted an exception, the webpage was able to provide a WebAuthn challenge that the user would be prompted to complete. This is in violation of the WebAuthN spec which requires "a secure transport established without errors". This vulnerability was fixed in Firefox 140 and Thunderbird 140.
How severe is CVE-2025-6433?: CVE-2025-6433 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2025-6433 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-6433?: CVE-2025-6433 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-6433?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2025-6433 have an EU (EUVD) identifier?: Yes. CVE-2025-6433 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-19088.
When was CVE-2025-6433 published?: CVE-2025-6433 was published on 2025-06-24 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*

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