Is CVE-2020-6820 in the CISA KEV catalog?

Yes. CVE-2020-6820 is on the CISA Known Exploited Vulnerabilities list, added 2021-11-03.

What is the CVSS severity of CVE-2020-6820?

CVE-2020-6820 has a CVSS v3 base score of 8.1 (HIGH).

What is the EPSS score for CVE-2020-6820?

CVE-2020-6820 has an EPSS score of 6.30% (93th percentile), estimating the probability of exploitation in the next 30 days.

CVE & CISA-KEV Catalog

CVE-2020-6820

HIGHCISA KEVEPSS 93th pctl

8.1

CVSS v3

NVD

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.

CWE-362Race Condition

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploit Intelligence

6.30%probability of exploitation in 30 days

93rdpercentile

High risk: more likely to be exploited than 93% of all known CVEs.

Known Exploited Vulnerability (CISA KEV)

Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

Mozilla Firefox and Thunderbird contain a race condition vulnerability when handling a ReadableStream under certain conditions. The race condition creates a use-after-free vulnerability, causing unspecified impacts.

Apply updates per vendor instructions.

Remediation due: 2022-05-03

References

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-11-04.