CVE-2021-29946

Mozilla: Port blocking could be bypassed

Severity Score

8.8

*CVSS v3.1

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

*Multiple Sources

Exploited in Wild

*KEV

Decision

*SSVC

Descriptions

Ports that were written as an integer overflow above the bounds of a 16-bit integer could have bypassed port blocking restrictions when used in the Alt-Svc header. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.

Los puertos que se escribieron como un desbordamiento de enteros por encima de los límites de un entero de 16 bits podrían haber omitido las restricciones de bloqueo de puertos cuando se usaron en la cabecera Alt-Svc. Esta vulnerabilidad afecta a Firefox ESR versiones anteriores a 78.10, Thunderbird versiones anteriores a 78.10 y Firefox versiones anteriores a 88

Mozilla Firefox is an open-source web browser, designed for standards compliance, performance, and portability. This update upgrades Firefox to version 78.10.0 ESR. Issues addressed include bypass, spoofing, and use-after-free vulnerabilities.

*Credits: N/A

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Attack Vector

Network

Attack Complexity

Medium

Authentication

None

Confidentiality

Partial

Integrity

Partial

Availability

Partial

* Common Vulnerability Scoring System

SSVC

Decision:-

Exploitation

Automatable

Tech. Impact

* Organization's Worst-case Scenario

Timeline

2021-04-01 CVE Reserved
2021-04-26 CVE Published
2024-08-03 CVE Updated
2025-11-21 EPSS Updated
---------- Exploited in Wild
---------- KEV Due Date
---------- First Exploit

CWE

CWE-190: Integer Overflow or Wraparound

CAPEC

References (5)

URL	Tag	Source

URL	Date	SRC

URL	Date	SRC

URL	Date	SRC
https://www.mozilla.org/security/advisories/mfsa2021-14	2021-06-25
https://www.mozilla.org/security/advisories/mfsa2021-15	2021-06-25
https://www.mozilla.org/security/advisories/mfsa2021-16	2021-06-25
https://access.redhat.com/security/cve/CVE-2021-29946	2021-04-26
https://bugzilla.redhat.com/show_bug.cgi?id=1951371	2021-04-26

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"				< 88.0 Search vendor "Mozilla" for product "Firefox" and version " < 88.0"		-		Affected
Mozilla Search vendor "Mozilla"		Firefox Esr Search vendor "Mozilla" for product "Firefox Esr"				< 78.10 Search vendor "Mozilla" for product "Firefox Esr" and version " < 78.10"		-		Affected
Mozilla Search vendor "Mozilla"		Thunderbird Search vendor "Mozilla" for product "Thunderbird"				< 78.10 Search vendor "Mozilla" for product "Thunderbird" and version " < 78.10"		-		Affected