CVE-2020-6820VulnerabilityPublished 11/03/2021Updated 10/24/2026

CVE-2020-6820: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

Affects Mozilla Firefox and ThunderbirdSource CISA KEV

Severity

High

No CVSS score published yet

Exploitation: Actively exploited – in CISA KEV since 11/03/2021
KEV deadline: 05/03/2022
EPSS: 7.1% chance of exploitation in 30 days – higher than 94% of CVEs

What to do

CISA required action

Apply updates per vendor instructions.

nvd.nist.gov/vuln/detail/CVE-2020-6820 (opens in a new tab)

Description

CVE-2020-6820 is a use-after-free vulnerability in Mozilla Firefox and Thunderbird caused by a race condition when handling a ReadableStream under certain conditions. This flaw can lead to memory corruption with unspecified impacts. The vulnerability has been exploited in the wild. No specific affected versions or patch information is provided in the available data.

Summary

Mozilla Firefox and Thunderbird contain a race condition vulnerability (CWE-362) in the handling of ReadableStream objects. This race condition results in a use-after-free condition, which can cause memory corruption and potentially lead to arbitrary code execution or application crashes. The vulnerability has been observed to be exploited in the wild. However, no detailed technical exploitation methods or impact scenarios are described in the provided information. No patch or remediation details are included in the source data.

Impact

Successful exploitation of this use-after-free vulnerability can lead to memory corruption, which may allow attackers to execute arbitrary code or cause denial of service by crashing the affected application. The exact impact is unspecified in the data but is considered high severity due to exploitation in the wild.

Mitigation

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no patch or official fix information is provided, users should monitor Mozilla security advisories for updates and apply any available updates promptly once released.

Weaknesses

CWE-362Race Condition (opens in a new tab)

What to do

Description

AnalysisAI-generated, updated 10/24/2026, 09:10:19 UTC

Weaknesses

References

Related threats