---
title: "CVE-2020-6819: Use After Free | CubePath"
description: "Under certain conditions, when running the nsDocShell destructor, a race condition can cause a use-after-free. We are aware of targeted attacks…"
language: en
source: https://cubepath.com/security/cve/CVE-2020-6819
---

# CVE-2020-6819: Use After Free | CubePath

## 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.

Official description from the CVE record, published by mozilla. Copyright © 1999-2026 The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CVE license. [View the record on cve.org](https://www.cve.org/CVERecord?id=CVE-2020-6819)

## Key data

### CVSS 3.1 High 8.1

Score published by CISA-ADP in the CVE record.

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

| Metric                 | Value     | What it means                                                                             |
| ---------------------- | --------- | ----------------------------------------------------------------------------------------- |
| Attack vector          | Network   | The vulnerable component can be reached over a network, possibly from the Internet.       |
| Attack complexity      | High      | The attack depends on conditions outside the attacker's control, so it takes preparation. |
| Privileges required    | None      | No account or privileges are needed.                                                      |
| User interaction       | None      | No action from any user is needed.                                                        |
| Scope                  | Unchanged | The impact stays within the vulnerable component.                                         |
| Confidentiality impact | High      | Serious or total effect on the secrecy of data.                                           |
| Integrity impact       | High      | Serious or total effect on the trustworthiness of data.                                   |
| Availability impact    | High      | Serious or total effect on availability.                                                  |

CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at [first.org/cvss](https://www.first.org/cvss/) .

### EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.

Score

0.03039 (3.0% probability)

Percentile

87.6%

Scores of

Nov 10, 2026

Model

v2026.06.15

### CISA Known Exploited Vulnerabilities

This CVE is listed in the CISA KEV catalog.

Name in the catalog

Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

Added to the catalog

Nov 3, 2021

Federal due date

May 3, 2022

### CISA assessment as of Feb 7, 2025

Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA.

Exploitation

Recorded by CISA as active

Automatable

no

Technical impact

total

### Weakness (CWE)

CWE catalog version 5.0.

CWE names: Copyright © 2006-2026, The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CWE license.

- [CWE-416](https://cwe.mitre.org/data/definitions/416.html) Use After Free

## Affected products

Products listed in the CVE record, as the CNA published them.

- Mozilla Thunderbird

  - affected: unspecified up to before 68.7.0
- Mozilla Firefox

  - affected: unspecified up to before 74.0.1
- Mozilla Firefox ESR

  - affected: unspecified up to before 68.6.1

## References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

- [mozilla.org/security/advisories/mfsa2020-14](https://www.mozilla.org/security/advisories/mfsa2020-14/)
- [mozilla.org/security/advisories/mfsa2020-11](https://www.mozilla.org/security/advisories/mfsa2020-11/)
- [bugzilla.mozilla.org/show\_bug.cgi?id=1620818](https://bugzilla.mozilla.org/show%5Fbug.cgi?id=1620818)
- [USN-4335-1](https://usn.ubuntu.com/4335-1/)  (usn.ubuntu.com) vendor-advisory

## Timeline

1. ID reserved Jan 10, 2020
2. Record published Apr 24, 2020
3. Added to CISA KEV Nov 3, 2021
4. Record last updated Oct 21, 2025

## Look up another CVE

## About CubePath

CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection.

[Cloud VPS](https://cubepath.com/vps) [DDoS protection](https://cubepath.com/ddos-protection)

Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:37 UTC. [Sources and licenses](https://cubepath.com/security/cve/legal)