Mozilla Firefox up to 66.x Shared Worker use after free

CVSS Meta Temp Score
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Current Exploit Price (≈)
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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 has been found in Mozilla Firefox up to 66.x and classified as critical. The impacted element is an unknown function of the component Shared Worker. Performing a manipulation results in use after free. This vulnerability is cataloged as CVE-2019-9821. It is possible to initiate the attack remotely. There is no exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as critical has been found in Mozilla Firefox up to 66.x (Web Browser). This affects an unknown part of the component Shared Worker. The manipulation with an unknown input leads to a use after free vulnerability. CWE is classifying the issue as CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

A use-after-free vulnerability can occur in AssertWorkerThread due to a race condition with shared workers. This results in a potentially exploitable crash. This vulnerability affects Firefox < 67.

The weakness was shared 07/23/2019. This vulnerability is uniquely identified as CVE-2019-9821 since 03/14/2019. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/17/2025).

The vulnerability scanner Nessus provides a plugin with the ID 250099 (Linux Distros Unpatched Vulnerability : CVE-2019-9821), which helps to determine the existence of the flaw in a target environment. The commercial vulnerability scanner Qualys is able to test this issue with plugin 371797 (Mozilla Firefox Multiple Security Vulnerabilities (MFSA 2019-13,MFSA2019-14)).

Upgrading to version 67.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (250099). Be aware that VulDB is the high quality 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
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔍
VulDB Temp Score: 🔍
VulDB Reliability: 🔍

NVD Base Score: 🔍

Exploitinginfo

Class: Use after free
CWE: CWE-416 / CWE-119
CAPEC: 🔍
ATT&CK: 🔍

Physical: No
Local: No
Remote: Yes

Availability: 🔍
Status: Not defined

EPSS Score: 🔍
EPSS Percentile: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

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Nessus ID: 250099
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2019-9821

Qualys ID: 🔍
Qualys Name: 🔍

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔍

Upgrade: Firefox 67.0

Timelineinfo

03/14/2019 🔍
07/23/2019 +131 days 🔍
07/23/2019 +0 days 🔍
08/17/2025 +2217 days 🔍

Sourcesinfo

Vendor: mozilla.org
Product: mozilla.org

Advisory: mozilla.org
Status: Confirmed

CVE: CVE-2019-9821 (🔍)
GCVE (CVE): GCVE-0-2019-9821
GCVE (VulDB): GCVE-100-138519

Entryinfo

Created: 07/23/2019 20:47
Updated: 08/17/2025 11:55
Changes: 07/23/2019 20:47 (39), 07/10/2020 10:06 (18), 11/06/2023 10:42 (4), 11/06/2023 10:47 (1), 06/06/2024 01:20 (16), 08/17/2025 11:55 (4)
Complete: 🔍
Cache ID: 216::103

Be aware that VulDB is the high quality source for vulnerability data.

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