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Fencer Vulns
medium 4.3

CVE-2025-6434 json

HTTPS-Only exception screen lacked anti-clickjacking delay

published 2025-06-24 16 mo ago modified 2026-09-30 39 d ago also EUVD-2025-21375

cvss
4.3
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 20%
public exploits
0
none known

Summary

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.

Patch / fix

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

ubuntu advisories UBUNTU-CVE-2025-6434

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

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-2025-6434 updated cvss 3.4

firefox: HTTPS-Only exception screen lacked anti-clickjacking delay

  • 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
no
Technical impact
partial
Assessed
16 mo ago

Exploit prediction

0.28% chance of exploitation in the next 30 days, higher than 20% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
CNA 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird

Classification

Weakness
  • CWE-1021 Improper Restriction of Rendered UI Layers or Frames

References

Sources

Fencer Vulns 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.