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Mozilla CVE-2025-6433

| EUVDEUVD-2025-19088 CRITICAL
Improper Certificate Validation (CWE-295)
2025-06-24 security@mozilla.org
Mozilla Information Disclosure
Critical
Disputed · 9.8 NVD
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Severity by source

Sources disagree (Low–Critical)
NVD PRIMARY
9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Ubuntu
MEDIUM
qualitative
SUSE
CRITICAL
qualitative
Red Hat
3.4 LOW
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

4
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
EUVD ID Assigned
Mar 15, 2026 - 22:36 euvd
EUVD-2025-19088
Analysis Generated
Mar 15, 2026 - 22:36 vuln.today
CVE Published
Jun 24, 2025 - 13:15 nvd
CRITICAL 9.8

DescriptionCVE.org

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 affects Firefox < 140 and Thunderbird < 140.

AnalysisAI

CVE-2025-6433 is a critical WebAuthn specification violation in Firefox and Thunderbird that allows attackers to present WebAuthn authentication challenges over non-secure TLS connections with user-granted exceptions. This bypasses the WebAuthn requirement for secure transport without errors, enabling credential theft and account compromise. Firefox < 140 and Thunderbird < 140 are affected; the network-based attack requires no privileges or user interaction beyond the initial certificate exception grant, resulting in a CVSS 9.8 critical rating.

Technical ContextAI

WebAuthn (Web Authentication) is a W3C standard for cryptographic authentication that explicitly mandates 'secure transport established without errors' per the specification's security requirements. The vulnerability exists in how Firefox and Thunderbird handle the TLS certificate validation state when processing WebAuthn challenges. Specifically, when a user grants a security exception for an invalid/self-signed TLS certificate (CWE-295: Improper Certificate Validation), the browser's WebAuthn API should refuse to process authentication challenges, but instead permits them. This violates the secure context requirement that WebAuthn operations must occur only over HTTPS connections with valid certificates. The affected CPE identifiers are: mozilla:firefox (versions <140) and mozilla:thunderbird (versions <140). The root cause is improper certificate validation logic (CWE-295) that fails to distinguish between 'valid certificate' and 'user-granted exception to invalid certificate' when evaluating WebAuthn secure context requirements.

RemediationAI

Immediate remediation: (1) Update Firefox to version 140 or later; (2) Update Thunderbird to version 140 or later. These versions contain patches that enforce proper WebAuthn secure context validation and reject WebAuthn challenges over TLS connections with invalid certificates (including user-granted exceptions). Short-term mitigations pending patching: (a) Avoid granting security exceptions for self-signed/invalid certificates on authentication-critical sites; (b) Users should review and revoke any suspicious security exceptions in browser settings; (c) System administrators should enforce certificate validation policies via GPO or equivalent mechanisms to prevent exception grants. Organizations should prioritize Firefox and Thunderbird patching in their vulnerability management programs given the critical CVSS score and the prevalence of these browsers in enterprise environments. No workarounds exist that preserve full WebAuthn functionality while mitigating the vulnerability.

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Same weakness CWE-295 – Improper Certificate Validation

View all
CVE-2015-3152 MEDIUM POC
5.9
CVE-2017-2800 CRITICAL POC
9.8
CVE-2014-1266 HIGH POC
7.4
CVE-2022-47758 CRITICAL POC
9.8
CVE-2025-68121 CRITICAL POC
10.0
CVE-2025-29331 CRITICAL POC
9.8
CVE-2025-32878 CRITICAL POC
9.8
CVE-2024-3738 CRITICAL POC
9.8

Same technique Information Disclosure

View all
CVE-2013-2251 CRITICAL POC
9.8
CVE-2017-5638 CRITICAL POC
9.8
CVE-2025-24813 CRITICAL POC
9.8
CVE-2015-1701 HIGH POC
7.8
CVE-2017-0147 HIGH POC
7.5
CVE-2014-6324 HIGH POC
8.8
CVE-2023-7028 CRITICAL POC
10.0
CVE-2017-0213 HIGH POC
7.3

Vendor StatusVendor

Ubuntu

Priority: Medium
firefox
Release Status Version
jammy not-affected code not present
noble not-affected code not present
oracular not-affected code not present
plucky not-affected code not present
upstream needs-triage -
questing not-affected code not present
thunderbird
Release Status Version
noble not-affected code not present
oracular not-affected code not present
plucky not-affected code not present
upstream released 140
questing not-affected code not present
jammy released 1:140.7.1+build1-0ubuntu0.22.04.1
mozjs38
Release Status Version
bionic needs-triage -
jammy DNE -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs52
Release Status Version
bionic ignored -
focal ignored -
jammy DNE -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs68
Release Status Version
focal ignored -
jammy DNE -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs78
Release Status Version
jammy ignored -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs91
Release Status Version
jammy ignored -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs102
Release Status Version
jammy ignored -
noble ignored -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs115
Release Status Version
jammy DNE -
noble ignored -
oracular ignored -
plucky ignored -
upstream needs-triage -
questing DNE -
USN-7991-1

Debian

firefox
Release Status Fixed Version Urgency
sid fixed 148.0.2-1 -
(unstable) fixed 140.0-1 -

SUSE

Severity: Critical
Product Status
Image SLES12-SP5-SAP-Azure-LI-BYOS-Production Image SLES12-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP4-SAP-Azure-LI-BYOS Image SLES15-SP4-SAP-Azure-LI-BYOS-Production Image SLES15-SP4-SAP-Azure-VLI-BYOS Image SLES15-SP4-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP5-SAP-Azure-LI-BYOS Image SLES15-SP5-SAP-Azure-LI-BYOS-Production Image SLES15-SP5-SAP-Azure-VLI-BYOS Image SLES15-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP6-SAP-Azure-LI-BYOS Image SLES15-SP6-SAP-Azure-LI-BYOS-Production Image SLES15-SP6-SAP-Azure-VLI-BYOS Image SLES15-SP6-SAP-Azure-VLI-BYOS-Production Image SLES15-SP7-SAP-Azure-LI-BYOS-Production Image SLES15-SP7-SAP-Azure-VLI-BYOS-Production Affected
SUSE Enterprise Storage 7.1 Fixed

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CVE-2025-6433 vulnerability details – vuln.today
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