CVE-2020-6819
Mozilla Firefox And Thunderbird Use-After-Free Vulnerability is confirmed as actively exploited and is listed in the CISA KEV catalog.
Required action
Apply updates per vendor instructions.
CISA notes
https://nvd.nist.gov/vuln/detail/CVE-2020-6819
Description
Under certain conditions, when running the nsDocShell destructor, 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.
Severity
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HExploitation Context
as of October 17, 2026- CISA added CVE-2020-6819 to the KEV catalog 558 days after its CVE record was published.
- It is one of 13 Mozilla entries in the CISA KEV catalog, and one of 3 added in 2021.
- Its current EPSS score (3.0%) is higher than that of 12% of CISA KEV entries.
Affected Products
| Vendor | Product | Affected versions |
|---|---|---|
| Mozilla | Mozilla Thunderbird | unspecified to <68.7.0 |
| Mozilla | Mozilla Firefox | unspecified to <74.0.1 |
| Mozilla | Mozilla Firefox ESR | unspecified to <68.6.1 |
References
4 LinksRecord Details
More from Mozilla
Mozilla Firefox and Thunderbird Denial-of-Service Vulnerability
Mozilla Firefox and Thunderbird Sandbox Escape Vulnerability
Mozilla Firefox And Thunderbird Type Confusion Vulnerability
Mozilla Firefox and Thunderbird Type Confusion Vulnerability
CVE record data © The MITRE Corporation, used under the CVE Terms of Use. Exploited-in-the-wild data from the CISA Known Exploited Vulnerabilities catalog (CC0). Exploit prediction scores by FIRST EPSS (first.org/epss). This site is not endorsed or certified by MITRE, NVD, CISA, or FIRST.