9.8
CRITICAL
CVSS 3.1
CVE-2026-84143
Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15
Overview
Description
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.
Details
INFO
Published Date :
Sept. 1, 2026, 1:20 p.m.
Last Modified :
Sept. 3, 2026, 6:17 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Scoring
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework
for assessing the severity of vulnerabilities in software and systems.
We collect and displays CVSS scores from various sources for each CVE.
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | CRITICAL | [email protected] | ||||
| CVSS 3.1 | CRITICAL | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
Solution
Update Firefox to the latest version to patch memory corruption vulnerabilities.
- Update Firefox to version 155.
- Update Firefox ESR to version 153.2.
- Update Firefox ESR to version 140.15.
References
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-84143.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-84143 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-84143
weaknesses.
CAPEC-8: Buffer Overflow in an API Call Buffer Overflow in an API Call
CAPEC-9: Buffer Overflow in Local Command-Line Utilities Buffer Overflow in Local Command-Line Utilities
CAPEC-10: Buffer Overflow via Environment Variables Buffer Overflow via Environment Variables
CAPEC-14: Client-side Injection-induced Buffer Overflow Client-side Injection-induced Buffer Overflow
CAPEC-24: Filter Failure through Buffer Overflow Filter Failure through Buffer Overflow
CAPEC-42: MIME Conversion MIME Conversion
CAPEC-44: Overflow Binary Resource File Overflow Binary Resource File
CAPEC-45: Buffer Overflow via Symbolic Links Buffer Overflow via Symbolic Links
CAPEC-46: Overflow Variables and Tags Overflow Variables and Tags
CAPEC-47: Buffer Overflow via Parameter Expansion Buffer Overflow via Parameter Expansion
CAPEC-100: Overflow Buffers Overflow Buffers
CAPEC-123: Buffer Manipulation Buffer Manipulation
CAPEC-13: Subverting Environment Variable Values Subverting Environment Variable Values
CAPEC-22: Exploiting Trust in Client Exploiting Trust in Client
CAPEC-59: Session Credential Falsification through Prediction Session Credential Falsification through Prediction
CAPEC-60: Reusing Session IDs (aka Session Replay) Reusing Session IDs (aka Session Replay)
CAPEC-79: Using Slashes in Alternate Encoding Using Slashes in Alternate Encoding
CAPEC-116: Excavation Excavation
CAPEC-169: Footprinting Footprinting
CAPEC-224: Fingerprinting Fingerprinting
CAPEC-285: ICMP Echo Request Ping ICMP Echo Request Ping
CAPEC-287: TCP SYN Scan TCP SYN Scan
CAPEC-290: Enumerate Mail Exchange (MX) Records Enumerate Mail Exchange (MX) Records
CAPEC-291: DNS Zone Transfers DNS Zone Transfers
CAPEC-292: Host Discovery Host Discovery
CAPEC-293: Traceroute Route Enumeration Traceroute Route Enumeration
CAPEC-294: ICMP Address Mask Request ICMP Address Mask Request
CAPEC-295: Timestamp Request Timestamp Request
CAPEC-296: ICMP Information Request ICMP Information Request
CAPEC-297: TCP ACK Ping TCP ACK Ping
CAPEC-298: UDP Ping UDP Ping
CAPEC-299: TCP SYN Ping TCP SYN Ping
CAPEC-300: Port Scanning Port Scanning
CAPEC-301: TCP Connect Scan TCP Connect Scan
CAPEC-302: TCP FIN Scan TCP FIN Scan
CAPEC-303: TCP Xmas Scan TCP Xmas Scan
CAPEC-304: TCP Null Scan TCP Null Scan
CAPEC-305: TCP ACK Scan TCP ACK Scan
CAPEC-306: TCP Window Scan TCP Window Scan
CAPEC-307: TCP RPC Scan TCP RPC Scan
CAPEC-308: UDP Scan UDP Scan
CAPEC-309: Network Topology Mapping Network Topology Mapping
CAPEC-310: Scanning for Vulnerable Software Scanning for Vulnerable Software
CAPEC-312: Active OS Fingerprinting Active OS Fingerprinting
CAPEC-313: Passive OS Fingerprinting Passive OS Fingerprinting
CAPEC-317: IP ID Sequencing Probe IP ID Sequencing Probe
CAPEC-318: IP 'ID' Echoed Byte-Order Probe IP 'ID' Echoed Byte-Order Probe
CAPEC-319: IP (DF) 'Don't Fragment Bit' Echoing Probe IP (DF) 'Don't Fragment Bit' Echoing Probe
CAPEC-320: TCP Timestamp Probe TCP Timestamp Probe
CAPEC-321: TCP Sequence Number Probe TCP Sequence Number Probe
CAPEC-322: TCP (ISN) Greatest Common Divisor Probe TCP (ISN) Greatest Common Divisor Probe
CAPEC-323: TCP (ISN) Counter Rate Probe TCP (ISN) Counter Rate Probe
CAPEC-324: TCP (ISN) Sequence Predictability Probe TCP (ISN) Sequence Predictability Probe
CAPEC-325: TCP Congestion Control Flag (ECN) Probe TCP Congestion Control Flag (ECN) Probe
CAPEC-326: TCP Initial Window Size Probe TCP Initial Window Size Probe
CAPEC-327: TCP Options Probe TCP Options Probe
CAPEC-328: TCP 'RST' Flag Checksum Probe TCP 'RST' Flag Checksum Probe
CAPEC-329: ICMP Error Message Quoting Probe ICMP Error Message Quoting Probe
CAPEC-330: ICMP Error Message Echoing Integrity Probe ICMP Error Message Echoing Integrity Probe
CAPEC-472: Browser Fingerprinting Browser Fingerprinting
CAPEC-497: File Discovery File Discovery
CAPEC-508: Shoulder Surfing Shoulder Surfing
CAPEC-573: Process Footprinting Process Footprinting
CAPEC-574: Services Footprinting Services Footprinting
CAPEC-575: Account Footprinting Account Footprinting
CAPEC-576: Group Permission Footprinting Group Permission Footprinting
CAPEC-577: Owner Footprinting Owner Footprinting
CAPEC-616: Establish Rogue Location Establish Rogue Location
CAPEC-643: Identify Shared Files/Directories on System Identify Shared Files/Directories on System
CAPEC-646: Peripheral Footprinting Peripheral Footprinting
CAPEC-651: Eavesdropping Eavesdropping
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-84143 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-84143 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 03, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Added CWE CWE-200 Added SSVC {'id': 'CVE-2026-84143', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-09-03T17:14:23.894743Z'} -
Initial Analysis by [email protected]
Sep. 03, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Added CWE CWE-119 Added CPE Configuration OR *cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* versions from (including) 154.0.0 up to (excluding) 155.0.0 *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* versions from (including) 154.0 up to (excluding) 155.0 *cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* versions up to (excluding) 140.15.0 *cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* versions from (including) 141.0.0 up to (excluding) 153.2.0 *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* versions up to (excluding) 140.15.0 *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* versions from (including) 141.0 up to (excluding) 153.2.0 Added Reference Type Mozilla Corporation: https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048793%2C2054645%2C2057114%2C2059109%2C2061287 Types: Issue Tracking Added Reference Type Mozilla Corporation: https://bugzilla.mozilla.org/buglist.cgi?bug_id=2054631%2C2054657%2C2055007%2C2055681%2C2057107%2C2058087%2C2058088%2C2058090%2C2058095%2C2058101%2C2059183%2C2059185%2C2061301%2C2061325 Types: Issue Tracking Added Reference Type Mozilla Corporation: https://bugzilla.mozilla.org/show_bug.cgi?id=2057108 Types: Issue Tracking Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-82/ Types: Vendor Advisory Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-84/ Types: Vendor Advisory Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-85/ Types: Vendor Advisory Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-86/ Types: Vendor Advisory Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-87/ Types: Vendor Advisory Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-88/ Types: Vendor Advisory -
CVE Modified by [email protected]
Sep. 01, 2026
Action Type Old Value New Value Changed Description Internally found bugs present in Firefox 154, Firefox ESR 153.1 and Firefox 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, and Firefox ESR 153.2. 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. Added Affected Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/84xxx/CVE-2026-84143.json">CVE-2026-84143</a> Added Reference https://www.mozilla.org/security/advisories/mfsa2026-86/ Added Reference https://www.mozilla.org/security/advisories/mfsa2026-87/ Added Reference https://www.mozilla.org/security/advisories/mfsa2026-88/ -
New CVE Received by [email protected]
Sep. 01, 2026
Action Type Old Value New Value Added Description Internally found bugs present in Firefox 154, Firefox ESR 153.1 and Firefox 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, and Firefox ESR 153.2. Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/84xxx/CVE-2026-84143.json">CVE-2026-84143</a> Added Reference https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048793%2C2054645%2C2057114%2C2059109%2C2061287 Added Reference https://bugzilla.mozilla.org/buglist.cgi?bug_id=2054631%2C2054657%2C2055007%2C2055681%2C2057107%2C2058087%2C2058088%2C2058090%2C2058095%2C2058101%2C2059183%2C2059185%2C2061301%2C2061325 Added Reference https://bugzilla.mozilla.org/show_bug.cgi?id=2057108 Added Reference https://www.mozilla.org/security/advisories/mfsa2026-82/ Added Reference https://www.mozilla.org/security/advisories/mfsa2026-84/ Added Reference https://www.mozilla.org/security/advisories/mfsa2026-85/
EPSS is a daily estimate of the probability of exploitation activity
being observed over the next 30 days. Following chart shows the EPSS
score history of the vulnerability.