CVE Watch—

CVE-2020-6820

Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

CVSS

—

No CVSS

EPSS

6.3%

p93

KEV

YES

Nov 3, 2021

Exploit Today

0-100

Published: — · Last modified: —

EPSS · 30d

6.3%EPSS · 30 days6.3%

2026-06-302026-07-16

KEV catalog record

Product

Mozilla / Firefox and Thunderbird

Vulnerability

Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

Added to KEV

Nov 3, 2021

Remediate by

May 3, 2022

Known ransomware use

Summary description

Mozilla Firefox and Thunderbird contain a race condition vulnerability when handling a ReadableStream under certain conditions. The race condition creates a use-after-free vulnerability, causing unspecified impacts.

Required action

Apply updates per vendor instructions.

Notes

https://nvd.nist.gov/vuln/detail/CVE-2020-6820

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