CVE-2020-6819 — Mozilla
HIGHCVE-2020-6819 is a high-severity (CVSS 8.1) CWE-362 vulnerability. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) — treat it as actively exploited and patch now. No vendor fix is recorded yet; mitigation options are listed below.
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03. Federal agencies were required to remediate by 2022-05-03.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2020-6819.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-6819 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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.
Affected Products
firefoxmozillathunderbirdmozillaResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Under certain conditions, when running the nsDocShell destructor, a race…
Under certain conditions, when running the nsDocShell destructor, a race…
Under certain conditions, when running the nsDocShell destructor, a race…
Under certain conditions, when running the nsDocShell destructor, a race…
Detection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Remediation status
No fixed release is recorded for CVE-2020-6819 yet. Track the upstream advisory, and apply the exposure-reduction steps below in the meantime.
Mitigate without a patch
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 6 | firefox-0:68.6.1-1.el6_10 | RHSA-2020:1339 |
| Red Hat Enterprise Linux 6 | thunderbird-0:68.7.0-1.el6_10 | RHSA-2020:1488 |
| Red Hat Enterprise Linux 7 | firefox-0:68.6.1-1.el7_8 | RHSA-2020:1338 |
| Red Hat Enterprise Linux 7 | thunderbird-0:68.7.0-1.el7_8 | RHSA-2020:1489 |
| Red Hat Enterprise Linux 8 | firefox-0:68.6.1-1.el8_1 | RHSA-2020:1341 |
| Red Hat Enterprise Linux 8 | thunderbird-0:68.7.0-1.el8_1 | RHSA-2020:1495 |
| Red Hat Enterprise Linux 8.0 Update Services for SAP Solutions | firefox-0:68.6.1-1.el8_0 | RHSA-2020:1340 |
| Red Hat Enterprise Linux 8.0 Update Services for SAP Solutions | thunderbird-0:68.7.0-1.el8_0 | RHSA-2020:1496 |
Frequently Asked Questions
Is CVE-2020-6819 in your dependencies?
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