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9.8
CRITICAL CVSS 3.1
CVE-2026-4721
Memory safety bugs fixed in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149
Overview
Description

Memory safety bugs present in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Details
INFO

Published Date :

March 24, 2026, 1:16 p.m.

Last Modified :

April 13, 2026, 3:17 p.m.

Remotely Exploit :

Yes !

Source :

[email protected]
Impact
Affected Products

The following products are affected by CVE-2026-4721 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Mozilla firefox
2 Mozilla firefox_esr
3 Mozilla thunderbird
: Total Affected Vendor : 1 | Products : 3
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 3.1 CRITICAL 134c704f-9b21-4f2e-91b3-4a467353bcc0
Solution
Address memory safety bugs to prevent potential arbitrary code execution.
  • Update Firefox to version 149 or later.
  • Update Firefox ESR to version 115.34 or later.
  • Update Firefox ESR to version 140.9 or later.
  • Update Thunderbird to version 140.9 or later.
Public PoC/Exploit Available at Github

CVE-2026-4721 has a 1 public PoC/Exploit available at Github. Go to the Public Exploits tab to see the list.

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-2026-4721.

URL Resource
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2013762%2C2015291%2C2016591%2C2016661%2C2016664%2C2017303%2C2017894%2C2018090%2C2018196%2C2018379%2C2019112%2C2022090%2C2022243%2C2022351%2C2022478%2C2022676 Broken Link
https://www.mozilla.org/security/advisories/mfsa2026-20/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-21/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-22/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-23/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-24/ Vendor Advisory
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-4721 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-2026-4721 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-67: String Format Overflow in syslog() String Format Overflow in syslog() CAPEC-92: Forced Integer Overflow Forced Integer Overflow CAPEC-100: Overflow Buffers Overflow Buffers

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).

Profile Photo
w4zu/Debian_security

DSA and DLA for Debian last 14 days

Python

Updated: 1 week, 1 day ago
0 stars 0 fork 0 watcher
Born at : Feb. 12, 2025, 2:08 p.m. This repo has been linked 126 different CVEs too.

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-4721 vulnerability anywhere in the article.

  • CybersecurityNews
Firefox 149 Released With Patch for 37 Vulnerabilities that Enables Remote Attacks

Mozilla released Firefox 149 on March 24, 2026, delivering one of the largest security advisories in the browser’s recent history, addressing 37 vulnerabilities spanning memory corruption, sandbox esc ... Read more

Published Date: Mar 25, 2026 (2 weeks, 5 days ago)

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2026-4721 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 [email protected]

    Apr. 13, 2026

    Action Type Old Value New Value
    Changed Description Memory safety bugs present in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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 affects Firefox < 149, Firefox ESR < 115.34, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9. Memory safety bugs present in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
  • Initial Analysis by [email protected]

    Mar. 25, 2026

    Action Type Old Value New Value
    Added CPE Configuration OR *cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:* versions up to (excluding) 149.0 *cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:* versions up to (excluding) 115.34.0 *cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:* versions from (including) 128.0 up to (excluding) 140.9.0 *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:* versions up to (excluding) 149.0 *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:* versions up to (excluding) 140.9.0
    Added Reference Type Mozilla Corporation: https://bugzilla.mozilla.org/buglist.cgi?bug_id=2013762%2C2015291%2C2016591%2C2016661%2C2016664%2C2017303%2C2017894%2C2018090%2C2018196%2C2018379%2C2019112%2C2022090%2C2022243%2C2022351%2C2022478%2C2022676 Types: Broken Link
    Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-20/ Types: Vendor Advisory
    Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-21/ Types: Vendor Advisory
    Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-22/ Types: Vendor Advisory
    Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-23/ Types: Vendor Advisory
    Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-24/ Types: Vendor Advisory
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Mar. 25, 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-120
  • CVE Modified by [email protected]

    Mar. 24, 2026

    Action Type Old Value New Value
    Changed Description Memory safety bugs present in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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 affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9. Memory safety bugs present in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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 affects Firefox < 149, Firefox ESR < 115.34, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9.
    Added Reference https://www.mozilla.org/security/advisories/mfsa2026-23/
    Added Reference https://www.mozilla.org/security/advisories/mfsa2026-24/
  • New CVE Received by [email protected]

    Mar. 24, 2026

    Action Type Old Value New Value
    Added Description Memory safety bugs present in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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 affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9.
    Added Reference https://bugzilla.mozilla.org/buglist.cgi?bug_id=2013762%2C2015291%2C2016591%2C2016661%2C2016664%2C2017303%2C2017894%2C2018090%2C2018196%2C2018379%2C2019112%2C2022090%2C2022243%2C2022351%2C2022478%2C2022676
    Added Reference https://www.mozilla.org/security/advisories/mfsa2026-20/
    Added Reference https://www.mozilla.org/security/advisories/mfsa2026-21/
    Added Reference https://www.mozilla.org/security/advisories/mfsa2026-22/
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.
CVSS
Vulnerability Scoring Details
Base CVSS Score: 9.8
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact