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CVE-2026-84142

Internally found bugs fixed in Thunderbird 155

9.8 Critical

Internally found bugs present in Thunderbird 154. 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 and Thunderbird 155.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

0.56%Up 0.4 points since Sep 2, 2026
90%50%10%1%

What each source reports

NVD Score used9.8

Internally found bugs present in Thunderbird 154. 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 and Thunderbird 155.

Record
CVE-2026-84142
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-119, CWE-200
Updated
2026-11-02
CVE List9.8

Internally found bugs fixed in Thunderbird 155

Internally found bugs present in Thunderbird 154. 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 and Thunderbird 155.

Record
CVE-2026-84142
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-200
Updated
2026-11-02
EUVDEUVD-2026-690909.8

Internally found bugs present in Thunderbird 154. 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 and Thunderbird 155.

Record
EUVD-2026-69090
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-jc69-hhhc-c4h99.8

Internally found bugs present in Firefox 154. Some of these bugs showed evidence of memory...

Internally found bugs present in Firefox 154. 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.

Record
GHSA-jc69-hhhc-c4h9
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-119, CWE-200
Updated
2026-11-02
OSVUBUNTU-CVE-2026-841429.8

Internally found bugs present in Thunderbird 154. 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 and Thunderbird 155.

Record
UBUNTU-CVE-2026-84142
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVopenSUSE-SU-2026:11677-1No score

MozillaFirefox-155.0-1.1 on GA media

These are all security issues fixed in the MozillaFirefox-155.0-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:11677-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mozjs52
Ubuntu:18.04:LTS
All versions, plus listed versions
52.3.1-0ubuntu352.3.1-7fakesync152.8.1-0ubuntu0.18.04.152.9.1-0ubuntu0.18.04.1
None known
mozjs38
Ubuntu:18.04:LTS
All versions, plus listed versions
38.8.0~repack1-0ubuntu138.8.0~repack1-0ubuntu338.8.0~repack1-0ubuntu4
None known
mozjs68
Ubuntu:20.04:LTS
All versions, plus listed versions
68.5.0-1~fakesync68.5.0-2~fakesync68.6.0-168.6.0-1ubuntu1
None known
mozjs52
Ubuntu:20.04:LTS
All versions, plus listed versions
52.9.1-1build152.9.1-1ubuntu3
None known
mozjs102
Ubuntu:22.04:LTS
All versions, plus listed versions
102.11.0-0ubuntu0.22.04.1102.12.0-0ubuntu0.22.04.1102.13.0-0ubuntu0.22.04.1102.15.1-0ubuntu0.22.04.1
None known
mozjs78
Ubuntu:22.04:LTS
All versions, plus listed versions
78.13.0-178.15.0-278.15.0-4ubuntu1
None known
mozjs91
Ubuntu:22.04:LTS
All versions, plus listed versions
91.5.1-0ubuntu191.6.0-191.6.0-291.7.0-291.10.0-0ubuntu1
None known
thunderbird
Ubuntu:22.04:LTS
All versions, plus listed versions
1:91.1.2+build1-0ubuntu11:91.3.0+build2-0ubuntu11:91.3.1+build1-0ubuntu11:91.3.2+build1-0ubuntu11:91.4.0+build1.1-0ubuntu1
Show 34 moreShow less
1:91.4.0+build2-0ubuntu11:91.5.0+build1-0ubuntu11:91.5.1+build1-0ubuntu11:91.6.1+build1-0ubuntu11:91.7.0+build1-0ubuntu11:91.7.0+build2-0ubuntu11:91.8.0+build2-0ubuntu11:91.9.1+build1-0ubuntu0.22.04.11:91.11.0+build2-0ubuntu0.22.04.11:102.2.2+build1-0ubuntu0.22.04.11:102.4.2+build2-0ubuntu0.22.04.11:102.7.1+build2-0ubuntu0.22.04.11:102.8.0+build2-0ubuntu0.22.04.11:102.9.0+build1-0ubuntu0.22.04.11:102.10.0+build2-0ubuntu0.22.04.11:102.11.0+build1-0ubuntu0.22.04.11:102.13.0+build1-0ubuntu0.22.04.11:102.15.0+build1-0ubuntu0.22.04.11:102.15.1+build1-0ubuntu0.22.04.11:115.3.1+build1-0ubuntu0.22.04.21:115.4.1+build1-0ubuntu0.22.04.11:115.5.0+build1-0ubuntu0.22.04.11:115.6.0+build2-0ubuntu0.22.04.11:115.8.1+build1-0ubuntu0.22.04.11:115.9.0+build1-0ubuntu0.22.04.11:115.10.1+build1-0ubuntu0.22.04.11:115.11.0+build2-0ubuntu0.22.04.11:115.12.0+build3-0ubuntu0.22.04.11:115.13.0+build5-0ubuntu0.22.04.11:115.15.0+build1-0ubuntu0.22.04.11:115.16.0+build2-0ubuntu0.22.04.11:115.18.0+build1-0ubuntu0.22.04.11:128.12.0+build1-0ubuntu0.22.04.11:140.7.1+build1-0ubuntu0.22.04.1
None known
mozjs102
Ubuntu:24.04:LTS
All versions, plus listed versions
102.15.1-1102.15.1-3ubuntu2
None known
mozjs115
Ubuntu:24.04:LTS
All versions, plus listed versions
115.3.0-0ubuntu1115.4.0-2115.5.0-1115.6.0-1115.7.0-4
Show 4 moreShow less
115.8.0-1115.9.0-1115.9.0-1build1115.10.0-1
None known
MozillaFirefox
openSUSE:Tumbleweed
From an advisory covering 29 CVEs
before 155.0-1.1
155.0-1.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-84142 is a critical vulnerability (CVSS 9.8) in Mozilla Firefox, published September 1, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.56%, the 47th percentile. No source names a fixed version.

References

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