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CVE-2020-6820CISA KEV

Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

CISA lists this Mozilla Firefox and Thunderbird vulnerability as known exploited. The vendor's advisory has the fixed versions.

CISA KEVVendor advisoryNVD

CISA catalog record

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.

Product
Firefox and Thunderbird
Added to KEV
3 Nov 2021
Federal remediation due
3 May 2022
Known ransomware use
Not reported

What changed

First observed 14 Oct 2026

No field changes in the recorded history.

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ChangeIntel

An IT change radar: releases, security, known issues, retirements, documentation changes, and service status from public sources. Every item links to supporting evidence; dates and statuses can change after they are read.

Sources read 14 Oct 16:59 UTC · 254 of 255 readable · 253 fully read · documentation 0/409 current

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