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Fencer Vulns
critical 9.8

CVE-2026-5731 json

Memory safety bugs fixed in Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2

published 2026-04-07 7 mo ago modified 2026-10-24 16 d ago also EUVD-2026-19610

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 29%
public exploits
0
none known

Summary

Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

Patch / fix

  • Red Hat Red Hat Enterprise Linux 10 0:140.9.1-1.el10_1
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support 0:140.9.1-1.el10_0
  • Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support 0:140.9.1-2.el7_9
  • Red Hat Red Hat Enterprise Linux 8 0:140.9.1-1.el8_10
  • Red Hat Red Hat Enterprise Linux 8.2 Advanced Update Support 0:140.9.1-1.el8_2
  • Red Hat Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support 0:140.9.1-1.el8_4
  • Red Hat Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On 0:140.9.1-1.el8_4
  • Red Hat Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support 0:140.9.1-1.el8_6
  • Red Hat Red Hat Enterprise Linux 8.6 Telecommunications Update Service 0:140.9.1-1.el8_6
  • Red Hat Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions 0:140.9.1-1.el8_6
  • Red Hat Red Hat Enterprise Linux 8.8 Telecommunications Update Service 0:140.9.1-1.el8_8
  • Red Hat Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions 0:140.9.1-1.el8_8
  • Red Hat Red Hat Enterprise Linux 9 0:140.9.1-1.el9_7
  • Red Hat Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions 0:140.9.1-1.el9_0
  • Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions 0:140.9.1-1.el9_2
  • Red Hat Red Hat Enterprise Linux 9.4 Extended Update Support 0:140.9.1-1.el9_4
  • Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support 0:140.9.1-1.el9_6
  • firefox-esr Debian 12 140.9.1esr-1~deb12u1
  • firefox-esr Debian 13 140.9.1esr-1~deb13u1
  • firefox-esr Debian 14 140.9.1esr-1
  • thunderbird Debian 12 1:140.9.1esr-1~deb12u1
  • thunderbird Debian 13 1:140.9.1esr-1~deb13u1
  • thunderbird Debian 14 1:140.9.1esr-1

debian advisories DEBIAN-CVE-2026-5731

  • thunderbird RHEL 10.1 140.9.1-1.el10_1
  • thunderbird RHEL 8 140.9.1-1.el8_10
  • thunderbird RHEL 9 140.9.1-1.el9_7
  • firefox RHEL 8 140.9.1-1.el8_10
  • firefox RHEL 9 140.9.1-1.el9_7
  • firefox-x11 RHEL 9 140.9.1-1.el9_7
  • firefox RHEL 10.1 140.9.1-1.el10_1
  • thunderbird RHEL 8.6 TUS, RHEL 8.6 E4S, RHEL 8.6 AUS 140.9.1-1.el8_6

red hat advisories RHSA-2026:15889RHSA-2026:14303RHSA-2026:14223RHSA-2026:13977RHSA-2026:13922RHSA-2026:13682

  • MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Module for Package Hub 15 SP7 140.9.1-150200.8.266.1
  • MozillaFirefox SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 140.9.1-150200.152.228.1
  • MozillaFirefox SLES for SAP applications 16.0, SLES 16.0 140.9.1-160000.1.1
  • MozillaFirefox SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 140.9.1-112.307.1

suse advisories SUSE-SU-2026:1379-1SUSE-SU-2026:1322-1SUSE-SU-2026:1273-1SUSE-SU-2026:21157-1

  • MozillaFirefox openSUSE Leap 16.0 140.9.1-160000.1.1
  • MozillaFirefox openSUSE Tumbleweed 149.0.2-1.1
  • MozillaThunderbird openSUSE Tumbleweed 140.9.1-1.1
  • firefox-esr openSUSE Tumbleweed 140.9.1-1.1

opensuse advisories openSUSE-SU-2026:20486-1openSUSE-SU-2026:10511-1openSUSE-SU-2026:10501-1openSUSE-SU-2026:10503-1

  • thunderbird AlmaLinux 10 140.9.1-1.el10_1.alma.1
  • thunderbird AlmaLinux 8 140.9.1-1.el8_10.alma.1
  • thunderbird AlmaLinux 9 140.9.1-1.el9_7.alma.1
  • firefox AlmaLinux 8 140.9.1-1.el8_10.alma.1
  • firefox AlmaLinux 9 140.9.1-1.el9_7.alma.1
  • firefox-x11 AlmaLinux 9 140.9.1-1.el9_7.alma.1
  • firefox AlmaLinux 10 140.9.1-1.el10_1

almalinux advisories ALSA-2026:9638ALSA-2026:9345ALSA-2026:8459ALSA-2026:8052ALSA-2026:7671ALSA-2026:7672

  • thunderbird Rocky Linux 10 140.9.1-1.el10_1
  • thunderbird Rocky Linux 8 140.9.1-1.el8_10
  • thunderbird Rocky Linux 9 140.9.1-1.el9_7
  • firefox Rocky Linux 8 140.9.1-1.el8_10
  • firefox Rocky Linux 10 140.9.1-1.el10_1
  • firefox Rocky Linux 9 140.9.1-1.el9_7

rocky linux advisories RLSA-2026:9638RLSA-2026:9345RLSA-2026:8459RLSA-2026:8052RLSA-2026:7672RLSA-2026:7671

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-2026-5731 updated cvss 8.8

thunderbird: firefox: Memory safety bugs fixed in Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2

  • Red Hat Enterprise Linux 6 firefox, thunderbird Red Hat Enterprise Linux 7 thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 rhel10/firefox-flatpak, rhel10/thunderbird-flatpak
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) firefox 140.9.1-1.el8_10, thunderbird 140.9.1-1.el8_10
    fixed: vendor fix RHSA-2026:8052
  • Red Hat Enterprise Linux AppStream (v. 9) firefox 140.9.1-1.el9_7, firefox-x11 140.9.1-1.el9_7, thunderbird 140.9.1-1.el9_7
    fixed: vendor fix RHSA-2026:7671
  • Red Hat Enterprise Linux AppStream (v. 10) firefox 140.9.1-1.el10_1, thunderbird 140.9.1-1.el10_1
    fixed: vendor fix RHSA-2026:7672
  • Red Hat Enterprise Linux AppStream AUS (v. 8.2) firefox 140.9.1-1.el8_2
    fixed: vendor fix RHSA-2026:11805
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) firefox 140.9.1-1.el8_4, thunderbird 140.9.1-1.el8_4
    fixed: vendor fix RHSA-2026:13600
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) firefox 140.9.1-1.el8_6, thunderbird 140.9.1-1.el8_6 Red Hat Enterprise Linux AppStream E4S (v.8.6) firefox 140.9.1-1.el8_6, thunderbird 140.9.1-1.el8_6
    fixed: vendor fix RHSA-2026:13683
show 10 more
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) firefox 140.9.1-1.el8_8, thunderbird 140.9.1-1.el8_8
    fixed: vendor fix RHSA-2026:13682
  • Red Hat Enterprise Linux AppStream E4S (v.9.0) firefox 140.9.1-1.el9_0, thunderbird 140.9.1-1.el9_0
    fixed: vendor fix RHSA-2026:13596
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) firefox 140.9.1-1.el9_2, firefox-x11 140.9.1-1.el9_2, thunderbird 140.9.1-1.el9_2
    fixed: vendor fix RHSA-2026:13922
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) firefox 140.9.1-1.el10_0, thunderbird 140.9.1-1.el10_0
    fixed: vendor fix RHSA-2026:13665
  • Red Hat Enterprise Linux AppStream EUS (v.9.4) firefox 140.9.1-1.el9_4, firefox-x11 140.9.1-1.el9_4, thunderbird 140.9.1-1.el9_4
    fixed: vendor fix RHSA-2026:13582
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) firefox 140.9.1-1.el9_6, firefox-x11 140.9.1-1.el9_6, thunderbird 140.9.1-1.el9_6
    fixed: vendor fix RHSA-2026:13583
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) firefox 140.9.1-1.el8_4, thunderbird 140.9.1-1.el8_4
    fixed: vendor fix RHSA-2026:13600
  • Red Hat Enterprise Linux AppStream TUS (v.8.6) firefox 140.9.1-1.el8_6, thunderbird 140.9.1-1.el8_6
    fixed: vendor fix RHSA-2026:13683
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) firefox 140.9.1-1.el8_8, thunderbird 140.9.1-1.el8_8
    fixed: vendor fix RHSA-2026:13682
  • Red Hat Enterprise Linux Server (v. 7 ELS) firefox 140.9.1-2.el7_9
    fixed: vendor fix RHSA-2026:13977

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
total
Assessed
7 mo ago

Exploit prediction

0.35% chance of exploitation in the next 30 days, higher than 29% of all scored CVEs (FIRST EPSS, 2026-11-08).

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
CISA ADP 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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
CNA 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 8.2 Advanced Update Support
  • Red Hat Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support
  • Red Hat Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On
  • Red Hat Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support
  • Red Hat Red Hat Enterprise Linux 8.6 Telecommunications Update Service
  • Red Hat Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 8.8 Telecommunications Update Service
  • Red Hat Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9.4 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7

Classification

Weakness
  • CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer
  • CWE-787 Out-of-bounds Write

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.