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Full vulnerability report · 2026
CVE-2026-84145High confidence

Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15

Mozilla · Firefox

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
Distribution package intelligence

Ubuntu vendor package status

Canonical’s release and source-package findings are shown separately from local repository availability.

2 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Ubuntu releaseSource packageVendor stateFixed versionEvidence
Ubuntu 24.04 LTSnoble · standard archivemozjs102Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical record ↗Source updated 10 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivemozjs115Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical record ↗Source updated 10 Sept 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-84145 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityfirefox: Internally found bugs fixed in Firefox 155, Firefox ESR 153.2, Firefox ESR 140.15 and Firefox ESR 115.40
23 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • firefox as a component of Red Hat Enterprise Linux 10
  • firefox.src as a component of Red Hat Enterprise Linux 10
  • rhel10/firefox-flatpak as a component of Red Hat Enterprise Linux 10
  • rhel10/thunderbird-flatpak as a component of Red Hat Enterprise Linux 10
  • thunderbird as a component of Red Hat Enterprise Linux 10
  • thunderbird.src as a component of Red Hat Enterprise Linux 10
  • firefox as a component of Red Hat Enterprise Linux 6
  • firefox.src as a component of Red Hat Enterprise Linux 6
  • thunderbird as a component of Red Hat Enterprise Linux 6
  • thunderbird.src as a component of Red Hat Enterprise Linux 6
  • firefox as a component of Red Hat Enterprise Linux 7
  • firefox.src as a component of Red Hat Enterprise Linux 7
Summary
A flaw was found in Firefox. The Mozilla Foundation's Security Advisory describes the following issue: Internally found bugs present in Firefox 154, Firefox ESR 153.1, Firefox ESR 140.14 and Firefox ESR 115.39. 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.
Remediation
Affected
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-69068

No EUVD known-exploited evidence

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 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.5 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

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 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

What

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 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Why

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

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 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Why

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Restriction of Operations within the Bounds of a Memory Buffer → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
Required interaction required
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-119 ↗

CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer. The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-119
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-69068Official EUVD mapping

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 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Official EUVD record
BSI · German · WID-SEC-W-2026-3132Mozilla Firefox und Thunderbird: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Mozilla Firefox und Thunderbird ausnutzen, um Berechtigungen zu erweitern, Sicherheitsmaßnahmen zu umgehen, sensible Informationen offenzulegen, Daten zu manipulieren, Spoofing-Angriffe durchzuführen, möglicherweise durch Speicherbeschädigungen beliebigen Code auszuführen oder Denial-of-Service-Zustände herbeizuführen.

Official advisory
CERT-FR · French · CERTFR-2026-AVI-1106Multiples vulnérabilités dans les produits Mozilla

d?id=CVE-2026-84136 Référence CVE CVE-2026-84137 https://www.cve.org/CVERecord?id=CVE-2026-84137 Référence CVE CVE-2026-84138 https://www.cve.org/CVERecord?id=CVE-2026-84138 Référence CVE CVE-2026-84139 https://www.cve.org/CVERecord?id=CVE-2026-84139 Référence CVE CVE-2026-84140 https://www.cve.org/CVERecord?id=CVE-2026-84140 Référence CVE CVE-2026-84141 https://www.cve.org/CVERecord?id=CVE-2026-84141 Référence CVE CVE-2026-84142 https://www.cve.org/CVERecord?id=CVE-2026-84142 Référence CVE CVE-2026-84143 https://www.cve.org/CVERecord?id=CVE-2026-84143 Référence CVE CVE-2026-84144 https://www.cve.org/CVERecord?id=CVE-2026-84144 Référence CVE CVE-2026-84145 https://www.cve.org/CVERecord?id=CVE-2026-84145 Référence CVE CVE-2026-84637 https://www.cve.org/CVERecord?id=CVE-2026-84637 Référence CVE CVE-2026-84639 https://www.cve.org/CVERecord?id=CVE-2026-84639 Référence CVE CVE-2026-84640 https://www.cve.org/CVERecord?id=CVE-2026-84640 Référence CVE CVE-2026-84641 https://www.cve.org/CVERecord?id=CVE-2026-84641 Référence CVE CVE-2026-84642 https://www.cve.org/CVERecord?id=CVE-2026-84642 Gestion détaillée du document le 02 septembre 2026 Version initiale Alertes Avis Bulletins d’actualités Mentions légales Conditions générales À propos Contact cyber.gouv.fr service-public.fr legifrance.gouv.fr info.g

Official advisory
CSIRT Italia · Italian · risolte-vulnerabilita-in-prodotti-mozilla-9Risolte vulnerabilità in prodotti Mozilla

Aggiornamenti di sicurezza sanano 11 vulnerabilità, di cui 3 con gravità “critica” e 8 con gravità “alta”, nei prodotti Firefox, Firefox ESR, Thunderbird.

Official advisory
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
firefox as a component of Red Hat Enterprise Linux 10; firefox.src as a component of Red Hat Enterprise Linux 10; rhel10/firefox-flatpak as a component of Red Hat Enterprise Linux 10; rhel10/thunderbird-flatpak as a component of Red Hat Enterprise Linux 10; thunderbird as a component of Red Hat Enterprise Linux 10; thunderbird.src as a component of Red Hat Enterprise Linux 10; firefox as a component of Red Hat Enterprise Linux 6; firefox.src as a component of Red Hat Enterprise Linux 6; thunderbird as a component of Red Hat Enterprise Linux 6; thunderbird.src as a component of Red Hat Enterprise Linux 6; firefox as a component of Red Hat Enterprise Linux 7; firefox.src as a component of Red Hat Enterprise Linux 7; thunderbird as a component of Red Hat Enterprise Linux 7; thunderbird.src as a component of Red Hat Enterprise Linux 7; firefox as a component of Red Hat Enterprise Linux 8; firefox.src as a component of Red Hat Enterprise Linux 8; thunderbird as a component of Red Hat Enterprise Linux 8; thunderbird.src as a component of Red Hat Enterprise Linux 8; firefox as a component of Red Hat Enterprise Linux 9; firefox-x11 as a component of Red Hat Enterprise Linux 9; firefox.src as a component of Red Hat Enterprise Linux 9; thunderbird as a component of Red Hat Enterprise Linux 9; thunderbird.src as a component of Red Hat Enterprise Linux 9
Fixed
115.40 ≤ 115.*; 140.15 ≤ 140.*; 153.2 ≤ 153.*; 155 ≤ *
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 1 Sept 2026 · Last source change 2 Sept 2026, 03:55 UTC · CWE-119 · Improper Restriction of Operations within the Bounds of a Memory Buffer

CVE recordCVE.org · 5.2
CVSS sourceCISA ADP
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-09-02
European sourceENISA EUVD · EUVD-2026-69068
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCISA ADP
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →
  1. BlackTree coverageBlackTree article coverage changed from no BlackTree article to 1 BlackTree article.
    Before
    no BlackTree article
    After
    1 BlackTree article
    BlackTree editorial ↗
  2. Vendor guidanceAuthoritative vendor guidance changed from authoritative remediation link to authoritative remediation link · vendor advisory.
    Before
    authoritative remediation link
    After
    authoritative remediation link · vendor advisory
    security@mozilla.org ↗
  3. ENISA EUVD mappingEUVD-2026-69068 was added to the official ENISA EUVD mapping for this CVE.
    Before
    not recorded
    After
    {"euvdId":"EUVD-2026-69068"}
    ENISA EUVD ↗
  4. Vendor guidanceAuthoritative vendor guidance changed from authoritative remediation link to authoritative remediation link.
    Before
    authoritative remediation link
    After
    authoritative remediation link
    CNA ↗
  5. Vendor guidanceAuthoritative vendor guidance changed from authoritative remediation link to authoritative remediation link.
    Before
    authoritative remediation link
    After
    authoritative remediation link
    CNA ↗
  6. SeveritySeverity changed from Unknown to High.
    Before
    Unknown
    After
    High
    CISA ADP ↗
  7. CVSS scoreCVSS score changed from not recorded to 7.5 (CVSS 3.1 · CISA ADP · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H).
    Before
    not recorded
    After
    7.5 (CVSS 3.1 · CISA ADP · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H)
    CISA ADP ↗
  8. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-69068↗Vendor CSAF · Red Hat Product Security↗Vendor advisory↗Vendor advisory↗Vendor advisory↗Vendor advisory↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-84145 · cve.blacktree.nl