CVE-2021-4129

Mozilla: Memory safety bugs fixed in Firefox 95 and Firefox ESR 91.4

Severity Score

9.8

*CVSS v3.1

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

*Multiple Sources

Exploited in Wild

*KEV

Decision

Attend

*SSVC

Descriptions

Mozilla developers and community members Julian Hector, Randell Jesup, Gabriele Svelto, Tyson Smith, Christian Holler, and Masayuki Nakano reported memory safety bugs present in Firefox 94. 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 < 95, Firefox ESR < 91.4.0, and Thunderbird < 91.4.0.

Los desarrolladores de Mozilla y miembros de la comunidad Julian Hector, Randell Jesup, Gabriele Svelto, Tyson Smith, Christian Holler y Masayuki Nakano informaron sobre errores de seguridad de la memoria presentes en Firefox 94. Algunos de estos errores mostraron evidencia de corrupción de la memoria y suponemos que con suficiente esfuerzo algunos de estos podrían haber sido explotados para ejecutar código arbitrario. Esta vulnerabilidad afecta a Firefox < 95, Firefox ESR < 91.4.0 y Thunderbird < 91.4.0.

The Mozilla Foundation Security Advisory describes this flaw as: Mozilla developers and community members Julian Hector, Randell Jesup, Gabriele Svelto, Tyson Smith, Christian Holler, and Masayuki Nakano reported memory safety bugs present in Thunderbird 91.3. 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.

Multiple vulnerabilities have been found in Mozilla Thunderbird, the worst of which could result in the arbitrary execution of code. Versions less than 91.12.0 are affected.

*Credits: N/A

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Attack Vector

Network

Attack Complexity

Low

Authentication

None

Confidentiality

Complete

Integrity

Complete

Availability

Complete

* Common Vulnerability Scoring System

SSVC

Decision:Attend

Exploitation

None

Automatable

Yes

Tech. Impact

Total

* Organization's Worst-case Scenario

Timeline

2021-12-16 CVE Reserved
2022-08-10 CVE Published
2025-03-30 EPSS Updated
2025-04-16 CVE Updated
2025-04-16 First Exploit
---------- Exploited in Wild
---------- KEV Due Date

CWE

CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
CWE-787: Out-of-bounds Write

CAPEC

References (6)

URL	Tag	Source

URL	Date	SRC
https://bugzilla.mozilla.org/buglist.cgi?bug_id=1393362%2C1736046%2C1736751%2C1737009%2C1739372%2C1739421	2025-04-16

URL	Date	SRC

URL	Date	SRC
https://www.mozilla.org/security/advisories/mfsa2021-52	2023-08-08
https://www.mozilla.org/security/advisories/mfsa2021-53	2023-08-08
https://www.mozilla.org/security/advisories/mfsa2021-54	2023-08-08
https://access.redhat.com/security/cve/CVE-2021-4129	2021-12-09
https://bugzilla.redhat.com/show_bug.cgi?id=2030116	2021-12-09

Affected Vendors, Products, and Versions

Vendor		Product				Version		Other		Status
Vendor	Product	Version	Other	Status	<-- -->	Vendor	Product	Version	Other	Status
Mozilla Search vendor "Mozilla"		Firefox Search vendor "Mozilla" for product "Firefox"				< 95.0 Search vendor "Mozilla" for product "Firefox" and version " < 95.0"		-		Affected
Mozilla Search vendor "Mozilla"		Firefox Esr Search vendor "Mozilla" for product "Firefox Esr"				< 91.4.0 Search vendor "Mozilla" for product "Firefox Esr" and version " < 91.4.0"		-		Affected
Mozilla Search vendor "Mozilla"		Thunderbird Search vendor "Mozilla" for product "Thunderbird"				< 91.4.0 Search vendor "Mozilla" for product "Thunderbird" and version " < 91.4.0"		-		Affected