CVE-2025-6433

Status: ModifiedCritical (9.8)—

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.

CVSS

Version: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Base score: 9.8

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days: 0.30%
Percentile among all scored CVEs: 20
Score date: 10/5/2026

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).

🎯 ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

ExploitationT1190 Exploit Public-Facing Applicationinitial access60 %
Primary impactT1557 Adversary-in-the-Middlecredential access · collection55 %

Inferred by deterministic rules from the CVSS vector and CWE. Indicative only.

🛡️ ATT&CK mitigations that cover these techniques

Network Segmentation Limit Access to Resource Over Network Filter Network Traffic Vulnerability Scanning User Training Privileged Account Management

Affected technologies (1)

Mozilla — Firefox

CWEs

CWE-295

References

Raw JSON (NVD)

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