Full Report
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.
Analysis Summary
# Vulnerability: Multiple Vulnerabilities in Mozilla Products (April 2026)
## CVE Details
- **CVE ID:** CVE-2026-5731, CVE-2026-5734, CVE-2026-5735 (Memory Safety); CVE-2026-5732 (Integer Overflow); CVE-2026-5733 (Boundary Condition)
- **CVSS Score:** Not explicitly provided, but rated as **High/Critical** severity by MS-ISAC due to RCE potential.
- **CWE:** CWE-119 (Memory Safety), CWE-190 (Integer Overflow).
## Affected Systems
- **Products:** Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR.
- **Versions:**
- Firefox: Prior to 149.0.2
- Firefox ESR: Prior to 140.9.1 and 115.34.1
- Thunderbird: Prior to 149.0.2
- Thunderbird ESR: Prior to 140.9.1
- **Configurations:** Systems where users operate with Administrative privileges are at highest risk.
## Vulnerability Description
Multiple security flaws exist within the Mozilla codebase, categorized primarily as **Memory Safety bugs**. The most critical vulnerabilities (CVE-2026-5731, CVE-2026-5734, and CVE-2026-5735) involve memory corruption issues that can be triggered during browser or email client operations. Additionally, CVE-2026-5732 and CVE-2026-5733 involve incorrect boundary conditions and integer overflows within the Graphics component.
## Exploitation
- **Status:** Not currently reported as exploited in the wild.
- **Complexity:** Medium (requires user interaction via drive-by compromise).
- **Attack Vector:** Network (Remote) via specialized web content or malicious emails.
## Impact
- **Confidentiality:** High (Attacker can view all user data).
- **Integrity:** High (Attacker can change/delete data or install programs).
- **Availability:** High (Attacker can delete data or create new accounts).
*Note: Successful exploitation allows for **Arbitrary Code Execution (RCE)** in the context of the current user.*
## Remediation
### Patches
Update to the following versions or higher:
- **Firefox:** 149.0.2
- **Firefox ESR:** 140.9.1 or 115.34.1
- **Thunderbird:** 149.0.2
- **Thunderbird ESR:** 140.9.1
### Workarounds
- **Principle of Least Privilege:** Operate software using non-privileged accounts to limit the scope of a potential compromise.
- **Disable Default Accounts:** Ensure administrator/root accounts are disabled or restricted.
## Detection
- **Indicators of Compromise:** Unusual program installations, unauthorized account creation, or unexpected outbound network traffic from browser processes.
- **Detection Methods:** Use Endpoint Detection and Response (EDR) clients or Host-based IPS agents to monitor for anomalous process executions steming from `firefox.exe` or `thunderbird.exe`.
## References
- **Vendor Advisories:**
- hxxps[://]www[.]mozilla[.]org/en-US/security/advisories/mfsa2026-25/
- hxxps[://]www[.]mozilla[.]org/en-US/security/advisories/mfsa2026-26/
- hxxps[://]www[.]mozilla[.]org/en-US/security/advisories/mfsa2026-27/
- **CVE Links:**
- hxxps[://]cve[.]mitre[.]org/cgi-bin/cvename[.]cgi?name=CVE-2026-5731
- hxxps[://]cve[.]mitre[.]org/cgi-bin/cvename[.]cgi?name=CVE-2026-5735