CVE-2020-6819

What the flaw is

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

Description as published by CISA. We have not independently reproduced it.

What CISA requires

Apply updates per vendor instructions.

This deadline is binding on US federal civilian agencies under BOD 22-01. It is not a legal deadline for anyone else, but it is a useful urgency signal — CISA sets it by how actively the flaw is being used, not by CVSS.

Public exploit code

3 public repositories referencing this CVE have been catalogued on GitHub. Treat this as a strong signal to prioritise patching, not as a verified working exploit — many such repositories are scanners, write-ups or forks rather than functional code.

• ARPSyndicate/cvemon
• Ostorlab/KEV
• Ostorlab/known_exploited_vulnerbilities_detectors

Vendor advisories

• nvd.nist.gov/vuln/detail/CVE-2020-6819

Primary sources

• NVD entry — CVSS score, CPE list and references
• CISA KEV catalog — the source for this page
• CVE Record at cve.org