{"id":"CVE-2020-6820","url":"https://www.cyber-defence.io/tools/cve/CVE-2020-6820","generatedAt":"2026-10-31T17:26:32.451Z","title":"Mozilla Firefox And Thunderbird Use-After-Free Vulnerability","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.","published":"2020-04-24T16:15:13.000Z","lastModified":"2026-06-17T03:23:52.000Z","status":"Analyzed","sourceIdentifier":"security@mozilla.org","cvss":{"version":"3.1","score":8.1,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H"},"cwe":["CWE-362"],"affected":["mozilla/firefox","mozilla/thunderbird"],"epss":{"score":0.07063,"percentile":0.94199,"date":"2026-10-30","history":[]},"kev":{"listed":true,"dateAdded":"2021-11-03","dueDate":"2022-05-03","knownRansomwareCampaignUse":"Unknown","notes":"Apply updates per vendor instructions.\nhttps://nvd.nist.gov/vuln/detail/CVE-2020-6820"},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"urgent","text":"Known to be exploited in the wild (CISA KEV, CISA remediation deadline 3 May 2022). Treat as an emergency change: patch or isolate now, then hunt for prior compromise."},"changes":[],"references":[{"url":"https://bugzilla.mozilla.org/show_bug.cgi?id=1626728","tags":["Issue Tracking","Permissions Required"],"source":"security@mozilla.org"},{"url":"https://usn.ubuntu.com/4335-1/","tags":["Third Party Advisory"],"source":"security@mozilla.org"},{"url":"https://www.mozilla.org/security/advisories/mfsa2020-11/","tags":["Vendor Advisory"],"source":"security@mozilla.org"},{"url":"https://www.mozilla.org/security/advisories/mfsa2020-14/","tags":["Vendor Advisory"],"source":"security@mozilla.org"},{"url":"https://bugzilla.mozilla.org/show_bug.cgi?id=1626728","tags":["Issue Tracking","Permissions Required"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://usn.ubuntu.com/4335-1/","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.mozilla.org/security/advisories/mfsa2020-11/","tags":["Vendor Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.mozilla.org/security/advisories/mfsa2020-14/","tags":["Vendor Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-6820","tags":["US Government Resource"],"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2020-6820","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}