CVE-2020-6820 Mozilla Firefox And Thunderbird Use-After-Free

What is CVE-2020-6820?

CVE-2020-6820 is a high-severity use after free vulnerability in Mozilla Firefox, published on 24 Apr 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Thunderbird < 68.7.0, Firefox < 74.0.1, and Firefox ESR < 68.6.1.

Weakness: CWE-362

Which versions are affected by CVE-2020-6820?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2020-6820?

Upgrade to a fixed version. US federal agencies must fix it by 3 May 2022.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2020-6820 being exploited?

Yes. Attackers have exploited CVE-2020-6820 in the wild since at least 3 Nov 2021.

Other vulnerabilities in Mozilla Firefox

• CVE-2019-11708 Mozilla Firefox and Thunderbird Sandbox Escape Exploited Critical 10.0
• CVE-2010-3765 Mozilla Multiple Products Remote Code Execution Exploited Critical 9.8
• CVE-2022-26486 Mozilla Firefox Use-After-Free Exploited Critical 9.6
• CVE-2022-26485 Mozilla Firefox Use-After-Free Exploited High 8.8
• CVE-2019-11707 Mozilla Firefox and Thunderbird Type Confusion Exploited High 8.8

All Mozilla Firefox vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2020-6820, GHSA-f77r-rqc9-53hh, UBUNTU-CVE-2020-6820.