CVE-2021-43535

Publication date 8 December 2021

Last updated 25 August 2025

Ubuntu priority

Cvss 3 Severity Score

Description

A use-after-free could have occured when an HTTP2 session object was released on a different thread, leading to memory corruption and a potentially exploitable crash. This vulnerability affects Firefox < 93, Thunderbird < 91.3, and Firefox ESR < 91.3.

Read the notes from the security team

Status

Show unmaintained releases

Package	Ubuntu Release	Status
firefox	23.04 lunar	Not affected
	22.10 kinetic	Not affected
	22.04 LTS jammy	Not affected
	21.10 impish	Not affected
	21.04 hirsute	Not affected
	20.04 LTS focal	Not in release
	18.04 LTS bionic	Not affected
	16.04 LTS xenial	Ignored end of standard support, was needed
	14.04 LTS trusty	Not in release
thunderbird	23.04 lunar	Not affected
	22.10 kinetic	Not affected
	22.04 LTS jammy	Not affected
	21.10 impish	Not affected
	21.04 hirsute	Ignored end of life
	20.04 LTS focal	Fixed 1:91.5.0+build1-0ubuntu0.20.04.1
	18.04 LTS bionic	Fixed 1:91.5.0+build1-0ubuntu0.18.04.1
	16.04 LTS xenial	Ignored end of standard support, was needed
	14.04 LTS trusty	Not in release

Notes

tyhicks

mozjs contains a copy of the SpiderMonkey JavaScript engine

Severity score breakdown

Parameter	Value
Base score	8.8 · High
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	Required
Scope	Unchanged
Confidentiality	High
Integrity impact	High
Availability impact	High
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

References

Related Ubuntu Security Notices (USN)

USN-5248-1
Thunderbird vulnerabilities
21 January 2022