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Fencer Intel
critical 9.8

CVE-2025-6433 json

WebAuthn would allow a user to sign a challenge on a webpage with an invalid TLS certificate

published last yr. modified last mo. also EUVD-2025-19088

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits
0
none known

Summary

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.

Patch / fix

  • mozilla firefox 140
  • thunderbird Ubuntu 22.04 LTS 1:140.7.1+build1-0ubuntu0.22.04.1

ubuntu advisories UBUNTU-CVE-2025-6433

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Workstation Extension 15 SP6, SLE Module for Package Hub 15 SP7 +2 more 140.1.0-150200.8.230.1
  • MozillaFirefox-branding-SLE SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES for SAP 15 SP3 +12 more 140-150200.9.21.1
  • pipewire SLE Module for Package Hub 15 SP7, SLE Module for Package Hub 15 SP6 0.3.6-150200.3.11.1
  • pipewire SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE High Performance Computing 15 SP3-LTSS +1 more 0.3.24-150300.4.8.1
  • pipewire SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE High Performance Computing 15 SP4-LTSS +1 more 0.3.49-150400.3.7.1
  • pipewire SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 0.3.64-150500.3.7.2
  • MozillaFirefox SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES for SAP 15 SP3 +12 more 140.1.0-150200.152.193.1
  • xdg-desktop-portal SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE High Performance Computing 15 SP3-LTSS +1 more 1.8.0-150200.5.8.1

suse advisories SUSE-SU-2025:02546-1SUSE-SU-2025:02529-1SUSE-SU-2025:02339-1

  • MozillaThunderbird openSUSE Tumbleweed 140.1.0-1.1
  • firefox-esr openSUSE Tumbleweed 140.1.0-1.1
  • MozillaFirefox openSUSE Tumbleweed 140.0.2-1.1

opensuse advisories openSUSE-SU-2025:15383-1openSUSE-SU-2025:15371-1openSUSE-SU-2025:15325-1

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-6433 updated cvss 3.4

firefox: WebAuthn would allow a user to sign a challenge on a webpage with an invalid TLS certificate

  • Red Hat Enterprise Linux 6 firefox Red Hat Enterprise Linux 7 firefox Red Hat Enterprise Linux 8 firefox Red Hat Enterprise Linux 9 firefox, firefox-x11 Red Hat Enterprise Linux 10 firefox, firefox-flatpak
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
last yr.

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird

Classification

Weakness
  • CWE-295 Improper Certificate Validation

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.