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NVD / CVE Program· CNA mozilla

CVE-2026-84143: Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15

CriticalCVSS 9.8 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 39/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.37% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: firefox (AlmaLinux:10) 140.15.0-1.el10_2; thunderbird (AlmaLinux:10) 140.16.0-1.el10_2.alma.1; firefox (AlmaLinux:8) 140.15.0-1.el8_10.alma.1.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to firefox (AlmaLinux:10) 140.15.0-1.el10_2; thunderbird (AlmaLinux:10) 140.16.0-1.el10_2.alma.1; firefox (AlmaLinux:8) 140.15.0-1.el8_10.alma.1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Published
Sep 1, 2026
Updated
Sep 3, 2026
EPSS
0.3% · 32th percentile

Report tools

JSON

Action score

39

Monitor

Low priority for now.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-84143

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  • when exploit code appears or is weaponized
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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
mozillafirefox
mozillathunderbird

Versions reported by the vendor

Affected version ranges reported by the assigning authority (mozilla). Independent of NVD's CPE analysis and usually ahead of it.

  • Mozilla Firefox

    • 140.15 and later · up to and including 140.*not affected · rpm
    • 153.2 and later · up to and including 153.*not affected · rpm
    • 155 and laternot affected · rpm

  • Mozilla Thunderbird

    • 140.15 and later · up to and including 140.*not affected · rpm
    • 153.2 and later · up to and including 153.*not affected · rpm
    • 155 and laternot affected · rpm
Affected versions · NVD (6)

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • mozilla firefoxbefore 140.15.0
  • mozilla firefox141.0.0 and later · before 153.2.0
  • mozilla firefox154.0.0 and later · before 155.0.0
  • mozilla thunderbirdbefore 140.15.0
  • mozilla thunderbird141.0 and later · before 153.2.0
  • mozilla thunderbird154.0 and later · before 155.0

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:10firefoxbefore 140.15.0-1.el10_2140.15.0-1.el10_2
AlmaLinux:10thunderbirdbefore 140.16.0-1.el10_2.alma.1140.16.0-1.el10_2.alma.1
AlmaLinux:8firefoxbefore 140.15.0-1.el8_10.alma.1140.15.0-1.el8_10.alma.1
AlmaLinux:8thunderbirdbefore 140.16.0-1.el8_10.alma.1140.16.0-1.el8_10.alma.1
AlmaLinux:9firefoxbefore 140.15.0-1.el9_8.alma.1140.15.0-1.el9_8.alma.1
AlmaLinux:9firefox-x11before 140.15.0-1.el9_8.alma.1140.15.0-1.el9_8.alma.1
AlmaLinux:9thunderbirdbefore 140.16.0-1.el9_8.alma.1140.16.0-1.el9_8.alma.1
Debian:12firefox-esrbefore 140.15.0esr-1~deb12u1140.15.0esr-1~deb12u1
Debian:12thunderbirdbefore 1:140.15.0esr-1~deb12u11:140.15.0esr-1~deb12u1
Debian:13firefox-esrbefore 140.15.0esr-1~deb13u1140.15.0esr-1~deb13u1
Debian:13thunderbirdbefore 1:140.15.0esr-1~deb13u11:140.15.0esr-1~deb13u1
Debian:14firefox-esrbefore 140.15.0esr-1140.15.0esr-1
Debian:14thunderbirdbefore 1:153.2.0esr-11:153.2.0esr-1
openSUSE:TumbleweedMozillaThunderbirdbefore 140.15.0-1.1140.15.0-1.1
Red Hat:enterprise_linux_eus:10.0firefoxbefore 0:140.15.0-1.el10_00:140.15.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0firefox-debuginfobefore 0:140.15.0-1.el10_00:140.15.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0firefox-debugsourcebefore 0:140.15.0-1.el10_00:140.15.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0thunderbirdbefore 0:140.15.0-1.el10_00:140.15.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0thunderbird-debuginfobefore 0:140.15.0-1.el10_00:140.15.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0thunderbird-debugsourcebefore 0:140.15.0-1.el10_00:140.15.0-1.el10_0
Red Hat:enterprise_linux:10.2firefoxbefore 0:140.15.0-1.el10_20:140.15.0-1.el10_2
Red Hat:enterprise_linux:10.2firefox-debuginfobefore 0:140.15.0-1.el10_20:140.15.0-1.el10_2
Red Hat:enterprise_linux:10.2firefox-debugsourcebefore 0:140.15.0-1.el10_20:140.15.0-1.el10_2
Red Hat:enterprise_linux:10.2thunderbirdbefore 0:140.16.0-1.el10_20:140.16.0-1.el10_2

+62

Same product

mozilla: all records

Other highest-scoring records for the same primary product.

  • CVE-2010-3765Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x…KEV
    94Now
  • CVE-2019-11708Insufficient vetting of parameters passed with the Prompt:Open IPC message between child and parent processes can result in the…KEV
    87Now
  • CVE-2015-4495The PDF reader in Mozilla Firefox before 39.0.3, Firefox ESR 38.x before 38.1.1, and Firefox OS before 2.2 allows remote attackers to…KEV
    86Now

Published before and after this one in the same product

  • ← EarlierCVE-2026-84141Sep 1, 2026 · Integer overflow in the Graphics: ImageLib component
    39Monitor
  • ← EarlierCVE-2026-84142Sep 1, 2026 · Internally found bugs fixed in Thunderbird 155
    39Monitor
  • Later →CVE-2026-84144Sep 1, 2026 · Internally found bugs fixed in Thunderbird 155 and Thunderbird ESR 153.2
    30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:firefox140.15.0-1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:firefox-x11140.15.0-1.el9_8.alma.1 · AlmaLinux:9Package registry (OSV)
almalinux:thunderbird140.16.0-1.el9_8.alma.1 · AlmaLinux:9Package registry (OSV)
debian:firefox-esr140.15.0esr-1~deb12u1 · Debian:12Package registry (OSV)
debian:thunderbird1:140.15.0esr-1~deb12u1 · Debian:12Package registry (OSV)
opensuse:MozillaThunderbird140.15.0-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:firefox0:140.15.0-1.el10_2 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:firefox-debuginfo0:140.15.0-1.el10_2 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:firefox-debugsource0:140.15.0-1.el10_2 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:firefox-x110:140.15.0-1.el9_8 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:thunderbird0:140.16.0-1.el9_8 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:thunderbird-debuginfo0:140.16.0-1.el9_8 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:thunderbird-debugsource0:140.16.0-1.el9_8 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
rocky linux:firefox0:140.15.0-1.el10_2 · Rocky Linux:10Package registry (OSV)
rocky linux:thunderbird0:140.16.0-1.el9_8 · Rocky Linux:9Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-1636742 days apartSandbox escape due to invalid pointer in the Disability Access APIs component
    40Plan
  • CVE-2026-2776189 days apartSandbox escape due to incorrect boundary conditions in the Telemetry component in External Software
    40Plan
  • CVE-2026-2778189 days apartSandbox escape due to incorrect boundary conditions in the DOM: Core & HTML component
    40Plan
  • CVE-2026-841420 days apartInternally found bugs fixed in Thunderbird 155
    39Monitor
  • CVE-2026-7498714 days apartInternally found bugs fixed in Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154
    39Monitor
  • CVE-2026-7499014 days apartInternally found bugs fixed in Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154
    39Monitor

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Not on record for this CVE: patch commit or PR link · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

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

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

References

Show all references (8 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records