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

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.

8.1 HIGHEPSS 7.06%⚡ Known Exploited (CISA KEV)NVD: Analyzed

Last updated: 2026-06-17 03:23 UTC

OverviewCVSS details

8.1HIGHCVSS 3.1

Score source: NVD
NVD status: Analyzed
Published: Apr 24, 2020
Assigner: mozilla

Affected

Thunderbird (Mozilla)

Versions: before 68.7.0
Fixed in: 68.7.0

+2 more products →

Exploitation

Public exploit: None listed
CISA KEV: Listed · Nov 3, 2021
KEV due date: May 3, 2022
Ransomware use: Unknown
SSVC: Exploitation active · Automatable no · Impact total

EPSS · FIRST, scored Nov 7

7.06%chance of exploitation in 30 days

Higher than 94.24% of CVEs

CVSS 3.1 · NVD

8.1High

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

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

CVSS 2.0 · NVD

6.8Medium

AV:N/AC:M/Au:N/C:P/I:P/A:P

Attack vector: Network
Attack complexity: Medium
Authentication: None
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

NVD status: Analyzed

Overview Affected Products References

NVD CVE.org

Overview

Severity

Score	Severity	Version	Vector String
8.1	HIGH	3.1NVD	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
6.8	MEDIUM	2.0NVD	AV:N/AC:M/Au:N/C:P/I:P/A:P

CISA required action

⚡ Known exploited · remediation due May 3, 2022

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Details

CVE ID: CVE-2020-6820
Status: Analyzed
Assigner (CNA): mozilla
Published: Apr 24, 2020
Last modified: 2026-06-17 03:23 UTC
Weaknesses: CWE-362

Sources

Refreshed hourly from the sources above. Last fetched 2026-11-08 08:55 UTC.