CVE-2020-6819: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

Reference page built from the source records below, each shown as its source publishes it. Dataset version ref-870fbfd07234, updated 2026-11-02T23:39:54.475Z.

CISA Known Exploited Vulnerabilities

Name
Mozilla Firefox And Thunderbird Use-After-Free Vulnerability
Vendor
Mozilla
Product
Firefox and Thunderbird
Added to the catalog
2021-11-03
Due date for US federal agencies
2022-05-03
Weaknesses
CWE-362, CWE-416
Catalog version
2026.10.30

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.

Required action (CISA)

Apply updates per vendor instructions.

Ransomware use: CISA does not mark known use of this vulnerability in ransomware campaigns.

Links in CISA's notes

Read on 2026-11-02T23:39:54.475Z under licence cisa-kev-cc0@b0067899 from https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

NVD analysis

Status
Analyzed
Published
2020-04-24T16:15:13.370
Last modified
2026-06-17T03:23:51.823
Weaknesses
CWE-362, CWE-416

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.

MetricScoreSeverityVectorScored by
CVSS 3.18.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H[email protected] (Primary)
CVSS 3.18.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H134c704f-9b21-4f2e-91b3-4a467353bcc0 (Secondary)
CVSS 2.06.8MEDIUMAV:N/AC:M/Au:N/C:P/I:P/A:P[email protected] (Primary)

References

This product uses the NVD API but is not endorsed or certified by the NVD.

Read on 2026-11-02T23:41:43.468Z under licence nvd-api-terms-of-use@ff2a5288 from https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2020-6819

CVE record

Assigner
mozilla
State
PUBLISHED
Published
2020-04-24T15:56:56.000Z
Updated
2025-10-21T23:35:45.566Z
Problem types
Use-after-free while running the nsDocShell destructor

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.

References

Read on 2026-11-03T01:04:56.012Z under licence cve-terms-of-use@81bfa2f3 from https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2020/6xxx/CVE-2020-6819.json

Defensive techniques (MITRE D3FEND)

D3FEND maps these defensive techniques to the weakness (CWE) that NVD lists for this CVE, through the digital artifacts the weakness affects. D3FEND does not say they stop this vulnerability.

CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

D3FEND ontology version 1.6.0.

Read on 2026-11-02T23:56:12.176Z under licence d3fend-terms-of-use@f98cbc7e from https://d3fend.mitre.org/api/weakness/cwe/CWE-362.json

CWE-416: Use After Free

D3FEND ontology version 1.6.0.

Read on 2026-11-02T23:56:27.750Z under licence d3fend-terms-of-use@f98cbc7e from https://d3fend.mitre.org/api/weakness/cwe/CWE-416.json

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"The MITRE Corporation (MITRE) hereby grants you a non-exclusive, royalty-free license to use D3FEND for research, development, and commercial purposes. Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." Terms: https://d3fend.mitre.org/tou/

Sources and licences

  • CISA

    Source: CISA Catalog of Known Exploited Vulnerabilities, version 2026.10.30, CC0 1.0. Use of this data does not imply endorsement by CISA or DHS.

    CC0 1.0 Universal

  • National Vulnerability Database (NIST)

    This product uses the NVD API but is not endorsed or certified by the NVD.

    NVD API Terms of Use (NIST publications in the public domain, 17 U.S.C. 105)

  • CVE Program, The MITRE Corporation

    Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation. CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy.

    CVE Program Terms of Use ("CVE Usage" licence)

  • MITRE D3FEND

    MITRE D3FEND™ knowledge graph. © 2025 The MITRE Corporation.
    "The MITRE Corporation (MITRE) hereby grants you a non-exclusive, royalty-free license to use D3FEND for research, development, and commercial purposes. Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." Terms: https://d3fend.mitre.org/tou/

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Cite this page

Dragons Eye Ransomware Tracker, "CVE-2020-6819: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability",
entity page, dataset version ref-870fbfd07234, updated 2026-11-02T23:39:54.475Z,
https://ransomware-tracker.com/cve/CVE-2020-6819 (accessed 2026-11-03).
Underlying source: CISA Catalog of Known Exploited Vulnerabilities, version 2026.10.30.
Underlying source: National Vulnerability Database (NIST), CVE API 2.0, record last modified 2026-06-17T03:23:51.823.
Underlying source: CVE List (CVE Program, The MITRE Corporation), record updated 2025-10-21T23:35:45.566Z.
Underlying source: MITRE D3FEND, ontology version 1.6.0.

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