Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

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• cpe mozilla/firefoxversion unspecified
• cpe mozilla/thunderbirdversion unspecified
• vendor Mozilla Firefox and Thunderbirdversion unspecified

How to fix CVE-2020-6819

• Recommended remediation

  Apply updates per vendor instructions. CISA due date May 3, 2022.

• Official advisories

  • CISA KEV · cisa.gov
  • CVE.org · cve.org
  • FIRST EPSS · first.org
  • NIST NVD · nvd.nist.gov
  • VulnCheck KEV · vulncheck.com

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

1. Apr 24, 2020 · Catalog

   Detected

   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.

2. Nov 3, 2021 · CISA KEV

   Known exploited

   Apply updates per vendor instructions.

3. May 3, 2022 · CISA KEV

   Remediation due

   Apply updates per vendor instructions.

4. Jun 16, 2026 · Catalog

   Updated

   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.

Sources

• CISA KEVConfirmed exploitationCVE-2020-6819

  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.

  cisa.gov
• CVE.orgVulnerability recordCVE-2020-6819

  Official CVE identifier

  cve.org
• FIRST EPSSExploitation probabilityCVE-2020-6819

  30-day exploitation probability 3.0%

  first.org
• NIST NVDVulnerability recordCVE-2020-6819

  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.

  nvd.nist.gov
• VulnCheck KEVConfirmed exploitationCVE-2020-6819

  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.

  vulncheck.com

References

• Exploit · bugzilla.mozilla.org
• VulnCheck exploitation evidence · docs.google.com
• CISA note · nvd.nist.gov
• Third Party Advisory · usn.ubuntu.com
• VulnCheck exploitation evidence · cisa.gov
• Vendor Advisory · mozilla.org
• Vendor Advisory · mozilla.org

Freshness

Last verified in this catalog Oct 17, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.