How severe is CVE-2020-6819?

CVE-2020-6819 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2020-6819 being actively exploited?

Yes. CVE-2020-6819 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2020-6819?

CVE-2020-6819 primarily affects Mozilla Firefox. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2020-6819?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

Does CVE-2020-6819 have an EU (EUVD) identifier?

Yes. CVE-2020-6819 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2020-27963. It is also flagged as exploited in the EUVD (since 2021-11-03).

When was CVE-2020-6819 published?

CVE-2020-6819 was published on 2020-04-24 and last updated on 2026-06-17.

CVE-2020-6819

CVE-2020-6819 is a high-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 8.1. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2021-11-03). The underlying weakness is classified as CWE-362.

Key facts

Severity: High (CVSS 3.x base score 8.1)
CVSS v2: 6.8
EPSS exploit prediction: 3% (86th percentile)
Actively exploited: Yes — listed in CISA KEV (added 2021-11-03)
EU (EUVD) id: EUVD-2020-27963
EU exploitation: Flagged exploited in the ENISA EU Vulnerability Database (since 2021-11-03)
Weakness: CWE-362
Affected product: Mozilla Firefox
Published: 2020-04-24
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-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.
How severe is CVE-2020-6819?: CVE-2020-6819 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2020-6819 being actively exploited?: Yes. CVE-2020-6819 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2020-6819?: CVE-2020-6819 primarily affects Mozilla Firefox. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-6819?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2020-6819 have an EU (EUVD) identifier?: Yes. CVE-2020-6819 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2020-27963. It is also flagged as exploited in the EUVD (since 2021-11-03).
When was CVE-2020-6819 published?: CVE-2020-6819 was published on 2020-04-24 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

More vulnerabilities in Mozilla Firefox

CVE-2026-4725 — Critical (CVSS 10.0): Sandbox escape due to use-after-free in the Graphics: Canvas2D component. This vulnerability was fixed in Firefox 149…
CVE-2026-4692 — Critical (CVSS 10.0): Sandbox escape in the Responsive Design Mode component. This vulnerability was fixed in Firefox 149, Firefox ESR…
CVE-2026-4689 — Critical (CVSS 10.0): Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component. This vulnerability was…
CVE-2026-4688 — Critical (CVSS 10.0): Sandbox escape due to use-after-free in the Disability Access APIs component. This vulnerability was fixed in Firefox…
CVE-2026-2778 — Critical (CVSS 10.0): Sandbox escape due to incorrect boundary conditions in the DOM: Core & HTML component. This vulnerability was fixed in…
CVE-2026-2776 — Critical (CVSS 10.0): Sandbox escape due to incorrect boundary conditions in the Telemetry component in External Software. This vulnerability…

All CVEs affecting Mozilla Firefox →

Other CWE-362 (Race Condition) vulnerabilities

CVE-2022-27626 — Critical (CVSS 10.0): A vulnerability regarding concurrent execution using shared resource with improper synchronization ('Race Condition')…
CVE-2015-8556 — Critical (CVSS 10.0): Local privilege escalation vulnerability in the Gentoo QEMU package before 2.5.0-r1.
CVE-2014-0703 — Critical (CVSS 10.0): Cisco Wireless LAN Controller (WLC) devices 7.4 before 7.4.110.0 distribute Aironet IOS software with a race condition…
CVE-2010-1228 — Critical (CVSS 10.0): Multiple race conditions in the sandbox infrastructure in Google Chrome before 4.1.249.1036 have unspecified impact and…
CVE-2008-6598 — Critical (CVSS 10.0): Multiple race conditions in WANPIPE before 3.3.6 have unknown impact and attack vectors related to "bri restart logic."
CVE-2026-46137 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: ADD_ADDR rtx: fix potential…

Browse all CWE-362 (Race Condition) vulnerabilities →