{"id":"CVE-2020-6819","kind":"vulnerability","aliases":["CVE-2020-6819"],"related":[],"title":"Mozilla Firefox and Thunderbird: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability","description":"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.\n\nCISA required action: Apply updates per vendor instructions.","summary":"Mozilla Firefox and Thunderbird have a race condition in the nsDocShell destructor that causes a use-after-free. Sources say the impact is unspecified, but CISA lists it as actively exploited in the wild.","severity":"high","cvss":8.1,"epss":0.03039,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Mozilla Firefox and Thunderbird","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["desktop-users","exploited","firefox","thunderbird","vendor"],"not_affected_if":["unknown"],"how_to_check":"Check the installed Firefox or Thunderbird version (Help > About) against the fixed release in the Mozilla advisory; unknown whether the sources give an exact version.","fix":"Update Firefox and Thunderbird to a current release per vendor instructions (CISA required action).","status":"open","published_at":"2020-04-24T16:15:13+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:41:47+00:00","updated_at":"2026-10-23T21:57:34+00:00","category":"vendor","confidence":0.5,"triage":{"at":"2026-10-23T21:41:47Z","model":"claude-haiku-5-5","output":{"fix":"Update Firefox and Thunderbird to a current release per vendor instructions (CISA required action).","reach":"unknown","impact":"high","summary":"Mozilla Firefox and Thunderbird have a race condition in the nsDocShell destructor that causes a use-after-free. Sources say the impact is unspecified, but CISA lists it as actively exploited in the wild.","category":"vendor","who_cares":["firefox","thunderbird","desktop-users"],"confidence":0.5,"needs_auth":"unknown","worst_case":"Memory corruption in the browser could let attackers run code; exact impact unspecified.","analyst_note":"Find the fixed Firefox and Thunderbird versions and the Mozilla advisory for CVE-2020-6819, plus the exploitation details, since the sources give no version or impact.","how_to_check":"Check the installed Firefox or Thunderbird version (Help > About) against the fixed release in the Mozilla advisory; unknown whether the sources give an exact version.","needs_analyst":true,"not_affected_if":["unknown"],"user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000491,"input_tokens":2875,"output_tokens":407,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2020':15A,18A '-6819':16A,19A 'action':98C 'activ':61B 'and':22A 'appli':99C 'caus':44B,93C 'certain':81C 'cisa':57B,96C 'condit':38B,73C,82C,85C 'contain':70C 'creat':86C 'cve':14A,17A 'desktop':25B 'desktop-us':24B 'destructor':42B,79C 'exploit':27B,62B 'firefox':2A,6A,21A,28B,32B,67C 'free':12A,49B,91C 'impact':53B,95C 'instruct':103C 'list':58B 'mozilla':1A,5A,20A,31B,66C 'nsdocshel':41B,78C 'per':101C 'race':37B,72C,84C 'requir':97C 'run':76C 'say':51B 'sourc':50B 'thunderbird':4A,8A,23A,29B,34B,69C 'unspecifi':55B,94C 'updat':100C 'use':10A,47B,89C 'use-after-fre':9A,46B,88C 'user':26B 'vendor':30B,102C 'vulner':13A,74C,92C 'wild':65B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2020-04-24T16:15:13+00:00","kev":{"dateAdded":"2021-11-03","dueDate":"2022-05-03","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Unknown"},"cvss_vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","cvss_by":"nvd@nist.gov","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2020-6819","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2020-6819","severity":null,"published_at":"2021-11-03T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:53+00:00","fetched_at":"2026-10-25T12:39:25+00:00","note":null},{"source":"epss","external_id":"CVE-2020-6819","url":"https://api.first.org/data/v1/epss?cve=CVE-2020-6819","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-23T19:13:43+00:00","fetched_at":"2026-10-23T19:13:43+00:00","note":null},{"source":"nvd","external_id":"CVE-2020-6819","url":"https://nvd.nist.gov/vuln/detail/CVE-2020-6819","severity":null,"published_at":"2020-04-24T16:15:13+00:00","modified_at":"2026-06-17T03:23:51+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","fetched_at":"2026-10-23T21:57:34+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}