Mozilla Firefox 74.0.0/ESR 68.6.0 ReadableStream double free

CVSS Meta Temp Score
CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.
Current Exploit Price (≈)
Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.
CTI Interest Score
Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
7.0$0-$5k0.00

Summaryinfo

A vulnerability labeled as critical has been found in Mozilla Firefox 74.0.0/ESR 68.6.0. This affects an unknown function of the component ReadableStream Handler. The manipulation results in double free. This vulnerability is known as CVE-2020-6820. It is possible to launch the attack remotely. Furthermore, an exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as critical has been found in Mozilla Firefox 74.0.0/ESR 68.6.0 (Web Browser). Affected is an unknown part of the component ReadableStream Handler. The manipulation with an unknown input leads to a double free vulnerability. CWE is classifying the issue as CWE-415. The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The weakness was published 04/03/2020 by Francisco Alonso and Javier Marcos as MFSA 2020-11 as confirmed security advisory (Website). The advisory is shared for download at mozilla.org. This vulnerability is traded as CVE-2020-6820. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. Technical details are unknown but a private exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 07/29/2025).

It is declared as attacked. The vulnerability scanner Nessus provides a plugin with the ID 208627 (CentOS 7 : firefox (RHSA-2020:1338)), which helps to determine the existence of the flaw in a target environment. This issue was added on 11/03/2021 to the CISA Known Exploited Vulnerabilities Catalog with a due date of 05/03/2022:

Apply updates per vendor instructions.

Upgrading to version 74.0.1 or ESR 68.6.1 eliminates this vulnerability. A possible mitigation has been published immediately after the disclosure of the vulnerability.

The vulnerability is also documented in the databases at Zero-Day.cz (569), Tenable (208627) and EUVD (EUVD-2020-27964). Similar entry is available at VDB-152819. Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.2
VulDB Meta Temp Score: 7.0

VulDB Base Score: 6.3
VulDB Temp Score: 6.0
VulDB Vector: 🔍
VulDB Reliability: 🔍

NVD Base Score: 8.1
NVD Vector: 🔍

CVSSv2info

AVACAuCIA
💳💳💳💳💳💳
💳💳💳💳💳💳
💳💳💳💳💳💳
VectorComplexityAuthenticationConfidentialityIntegrityAvailability
UnlockUnlockUnlockUnlockUnlockUnlock
UnlockUnlockUnlockUnlockUnlockUnlock
UnlockUnlockUnlockUnlockUnlockUnlock

VulDB Base Score: 🔍
VulDB Temp Score: 🔍
VulDB Reliability: 🔍

NVD Base Score: 🔍

Exploitinginfo

Class: Double free
CWE: CWE-415 / CWE-119
CAPEC: 🔍
ATT&CK: 🔍

Physical: No
Local: No
Remote: Yes

Availability: 🔍
Access: Private
Status: Attacked

EPSS Score: 🔍
EPSS Percentile: 🔍

KEV Added: 🔍
KEV Due: 🔍
KEV Remediation: 🔍
KEV Ransomware: 🔍
KEV Notice: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

0-DayUnlockUnlockUnlockUnlock
TodayUnlockUnlockUnlockUnlock

Nessus ID: 208627
Nessus Name: CentOS 7 : firefox (RHSA-2020:1338)

Zero-Day.cz: 🔍

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

Reaction Time: 🔍
0-Day Time: 🔍
Exposure Time: 🔍

Upgrade: Firefox 74.0.1/ESR 68.6.1

Timelineinfo

01/10/2020 🔍
04/03/2020 +84 days 🔍
04/03/2020 +0 days 🔍
04/07/2020 +4 days 🔍
07/29/2025 +1938 days 🔍

Sourcesinfo

Vendor: mozilla.org
Product: mozilla.org

Advisory: MFSA 2020-11
Researcher: Francisco Alonso, Javier Marcos
Status: Confirmed

CVE: CVE-2020-6820 (🔍)
GCVE (CVE): GCVE-0-2020-6820
GCVE (VulDB): GCVE-100-152820
EUVD: 🔍
scip Labs: https://www.scip.ch/en/?labs.20161013
See also: 🔍

Entryinfo

Created: 04/07/2020 11:36
Updated: 07/29/2025 01:29
Changes: 04/07/2020 11:36 (48), 04/07/2020 11:41 (17), 10/07/2020 14:33 (1), 04/20/2024 08:43 (25), 07/02/2024 04:18 (2), 09/09/2024 22:29 (1), 10/13/2024 03:17 (2), 02/07/2025 14:45 (1), 05/09/2025 21:46 (3), 07/29/2025 01:29 (1)
Complete: 🔍
Cache ID: 216::103

Once again VulDB remains the best source for vulnerability data.

Discussion

No comments yet. Languages: en.

Please log in to comment.

◂ PreviousOverviewNext ▸

Want to know what is going to be exploited?

We predict KEV entries!