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Fencer Vulns
high 8.1

CVE-2025-6436 json

Memory safety bugs fixed in Firefox 140 and Thunderbird 140

published 2025-06-24 16 mo ago modified 2026-09-30 39 d ago also EUVD-2025-19098

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
4.3%
EPSS 4.3% chance of exploitation in 30 days, percentile 91%
public exploits
0
none known

Summary

Memory safety bugs present in Firefox 139 and Thunderbird 139. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

Patch / fix

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

ubuntu advisories UBUNTU-CVE-2025-6436

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-2025-6436 updated cvss 7.5

firefox: Memory safety bugs fixed in Firefox 140 and Thunderbird 140

  • 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
16 mo ago

Exploit prediction

4.26% chance of exploitation in the next 30 days, higher than 91% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird

Classification

Weakness
  • CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer

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.