CVE-2020-6819

Exp

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.

Published: 2020-04-24 Last update: 2025-11-04 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-6819 is rated Active Exploitation (77.8/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.36%). CISA KEV confirms active exploitation (added 2021-11-03) affecting Mozilla / Firefox and Thunderbird. a weakness (CWE-362) Unauthenticated remote administrative access may be possible. The CISA remediation deadline has passed—treat as an emergency patch priority.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

CISA KEV Record for CVE-2020-6819

Name: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability · CISA KEV detail

Exploit added: 2021-11-03

Action due: 2022-05-03

Required action: Apply updates per vendor instructions.

Public exploit references (Exploit-DB) for CVE-2020-6819

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2020-6819

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-17 0.29% 0.36% +0.07%
2 2025-11-21 0.19% 0.29% +0.10%
3 2025-11-18 — 0.19% —

Full EPSS history (17 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-6819

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.1 3.1 HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 5.9 [email protected]
8.1 3.1 HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0
6.8 2.0 MEDIUM
AV:N/AC:M/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 6.4 [email protected]

Weakness enumeration for CVE-2020-6819

OS Trackers for CVE-2020-6819

vendor priority summary link
alpine — CVE-2020-6819: 4 source package rows (firefox, firefox-esr, librewolf, thunderbird); 36 state rows across 7 repos (3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 30, open 6. https://security.alpinelinux.org/vuln/CVE-2020-6819
debian not yet assigned CVE-2020-6819 not yet assigned priority: Debian including 3 source packages (firefox, firefox-esr, thunderbird), 11 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 11. https://security-tracker.debian.org/tracker/CVE-2020-6819
gentoo normal CVE-2020-6819: 1 GLSA(s) (202004-07), 1 atom(s) (www-client/firefox); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2020-6819
redhat critical — https://access.redhat.com/security/cve/CVE-2020-6819
suse high CVE-2020-6819 severity important: SUSE including 78 source package names (MozillaFirefox-102.11.0-150200.152.87.1, MozillaFirefox-115.10.0-150200.152.134.1, …), 154 product×package rows across 46 product lines (HPE Helion OpenStack 8, SUSE Enterprise Storage 5, … (46 product lines)): Fixed 154. https://www.suse.com/security/cve/CVE-2020-6819/
ubuntu high CVE-2020-6819 high priority: Ubuntu including 2 source packages (firefox, thunderbird), 12 status rows across 6 suites (bionic, eoan, focal, trusty, upstream, xenial): released 10, DNE 2. https://ubuntu.com/security/CVE-2020-6819

Affected software / configurations for CVE-2020-6819

Vendor Product Version Raw CPE
mozilla firefox < 68.6.1 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla firefox < 74.0.1 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
mozilla thunderbird < 68.7.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

References for CVE-2020-6819

cvelogic Threat Intelligence