Home CIS Advisories Multiple Vulnerabilities in Mozilla Products Could Allow for Arbitrary Code Execution Multiple Vulnerabilities in Mozilla Products Could Allow for Arbitrary Code Execution MS-ISAC ADVISORY NUMBER: 2026-001 DATE(S) ISSUED: 01/13/2026 OVERVIEW: Multiple vulnerabilities have been discovered in Mozilla products, the most severe of which could allow for arbitrary code execution. Mozilla Firefox is a web browser used to access the Internet. Mozilla Firefox ESR is a version of the web browser intended to be deployed in large organizations. Mozilla Thunderbird is an email client. Mozilla Thunderbird ESR is a version of the email client intended to be deployed in large organizations. Successful exploitation of the most severe of these vulnerabilities could allow for arbitrary code execution. Depending on the privileges associated with the user an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than those who operate with administrative user rights. THREAT INTELLIGENCE: There are currently no reports of these vulnerabilities being exploited in the wild. SYSTEMS AFFECTED: Firefox versions prior to 147 Firefox ESR versions prior to 115.32 Firefox ESR versions prior to 140.7 Thunderbird versions prior to 147 Thunderbird ESR versions prior to 140.7 RISK: Government: Large and medium government entities HIGH Small government MEDIUM Businesses: Large and medium business entities HIGH Small business entities MEDIUM Home Users: LOW TECHNICAL SUMMARY: Multiple vulnerabilities have been discovered in Mozilla products, the most severe of which could allow for arbitrary code execution. Details of these vulnerabilities are as follows: Tactic: Initial Access (TA0001): Technique: Drive-by Compromise (T1189) * Mitigation bypass in the DOM: Security component. (CVE-2026-0877) * Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component. (CVE-2026-0878) * Sandbox escape due to incorrect boundary conditions in the Graphics component. (CVE-2026-0879) * Sandbox escape due to integer overflow in the Graphics component. (CVE-2026-0880) * Sandbox escape in the Messaging System component. (CVE-2026-0881) * Use-after-free in the IPC component. (CVE-2026-0882) * Memory safety bugs fixed in Firefox ESR 140.7, Thunderbird ESR 140.7, Firefox 147 and Thunderbird 147. (CVE-2026-0891) Additional lower severity vulnerabilities include: * Information disclosure in the Networking component. (CVE-2026-0883) * Use-after-free in the JavaScript Engine component. (CVE-2026-0884) * Use-after-free in the JavaScript: GC component. (CVE-2026-0885) * Incorrect boundary conditions in the Graphics component. (CVE-2026-0886) * Clickjacking issue, information disclosure in the PDF Viewer component. (CVE-2026-0887) * Information disclosure in the XML component. (CVE-2026-0888) * Denial-of-service in the DOM: Service Workers component. (CVE-2026-0889) * Spoofing issue in the DOM: Copy & Paste and Drag & Drop component. (CVE-2026-0890) * Memory safety bugs fixed in Firefox 147 and Thunderbird 147. (CVE-2026-0892) * Spoofing issue in the Downloads Panel component. (CVE-2025-14327) Successful exploitation of the most severe of these vulnerabilities could allow for arbitrary code execution. Depending on the privileges associated with the user an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than those who operate with administrative user rights. RECOMMENDATIONS: We recommend the following actions be taken: * Apply appropriate updates provided by Mozilla to vulnerable systems immediately after appropriate testing. (M1051: Update Software) o Safeguard 7.1: Establish and Maintain a Vulnerability Management Process: Establish and maintain a documented vulnerability management process for enterprise assets. Review and update documentation annually, or when significant enterprise changes occur that could impact this Safeguard. o Safeguard 7.4: Perform Automated Application Patch Management: Perform application updates on enterprise assets through automated patch management on a monthly, or more frequent, basis. o Safeguard 7.7: Remediate Detected Vulnerabilities: Remediate detected vulnerabilities in software through processes and tooling on a monthly, or more frequent, basis, based on the remediation process. o Safeguard 9.1: Ensure Use of Only Fully Supported Browsers and Email Clients: Ensure only fully supported browsers and email clients are allowed to execute in the enterprise, only using the latest version of browsers and email clients provided through the vendor. * Apply the Principle of Least Privilege to all systems and services. Run all software as a non-privileged user (one without adminis