Multiple vulnerabilities have been discovered in Mozilla Thunderbird, the most severe of which could allow for arbitrary code execution. Mozilla Thunderbird is a free and open-source cross-platform email client, personal information manager, news client, RSS and chat client. 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:

• Thunderbird versions prior to 115.0.1

RISK:

Government:

• Large and medium government entities: High
• Small government entities: Medium

Businesses:

• Large and medium business entities: High
• Small business entities: Medium

Home users: Low

TECHNICAL SUMMARY:
Multiple vulnerabilities have been discovered in Mozilla Thunderbird, the most severe of which could allow for arbitrary code execution. Details of these vulnerabilities are as follows:

Tactic: Initial Access (TA0001), Execution (TA0002);

Technique: Phishing (T1566), User Execution: Malicious File (T1204.002)

• A vulnerability in Mozilla's Thunderbird could allow an attacker to spoof email attachment file extensions on the targeted host. This vulnerability occurs due to the Text Direction Override Unicode Character being allowed in filenames. Successful exploitation of this vulnerability could allow for arbitrary code execution if an attacker entices a victim to download and run a executable file. (CVE-2023-3417)

Additional lower priority vulnerabilities include:

• A use-after-free vulnerability in Mozilla's Thunderbird could allow for DoS. (CVE-2923-3600)

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:

1. Apply appropriate updates provided by Mozilla to vulnerable systems immediately after appropriate testing. (M1051: Update Software)

• 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.
• 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.
• 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.
• 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.

2. Restrict use of certain websites, block downloads/attachments, block JavaScript, restrict browser extensions, etc. (M1021: Restrict Web-Based Content)

• Safeguard 2.7 : Allowlist Authorized Scripts: Use technical controls, such as digital signatures and version control, to ensure that only authorized scripts, such as specific .ps1, .py, etc., files, are allowed to execute. Block unauthorized scripts from executing. Reassessbi-annually, or more frequently.
• Safeguard 2.3 : Address Unauthorized Software: Ensure that unauthorized software is either removed from use on enterprise assets or receives a documented exception. Review monthly, or more frequently.
• Safeguard 9.3: Maintain and Enforce Network-Based URL Filters: Enforce and update network-based URL filters to limit an enterprise asset from connecting to potentially malicious or unapproved websites. Example implementations include category-based filtering, reputation-based filtering, or through the use of block lists. Enforce filters for all enterprise assets.
• Safeguard 9.6: Block Unnecessary File Types: Block unnecessary file types attempting to enter the enterprise’s email gateway.

3. Inform and educate users regarding the threats posed by hypertext links contained in emails or attachments especially from un-trusted sources. Remind users not to visit un-trusted websites or follow links provided by unknown or un-trusted sources. (M1017: User Training)

• Safeguard 14.1: Establish and Maintain a Security Awareness Program: Establish and maintain a security awareness program. The purpose of a security awareness program is to educate the enterprise’s workforce on how to interact with enterprise assets and data in a secure manner. Conduct training at hire and, at a minimum, annually. Review and update content annually, or when significant enterprise changes occur that could impact this Safeguard.
• Safeguard 14.2: Train Workforce Members to Recognize Social Engineering Attacks: Train workforce members to recognize social engineering attacks, such as phishing, pre-texting, and tailgating.
• Safeguard 14.6 : Train Workforce Members on Recognizing and Reporting Security Incidents: Train workforce members to be able to recognize a potential incident and be able to report such an incident.

4. Block execution of code on a system through application control, and/or script blocking. (M1038: Execution Prevention)

• Safeguard 2.5 : Allowlist Authorized Software: Use technical controls, such as application allowlisting, to ensure that only authorized software can execute or be accessed. Reassess bi-annually, or more frequently.
• Safeguard 2.6 : Allowlist Authorized Libraries: Use technical controls to ensure that only authorized software libraries, such as specific .dll, .ocx, .so, etc., files, are allowed to load into a system process. Block unauthorized libraries from loading into a system process. Reassess bi-annually, or more frequently.
• Safeguard 2.7 : Allowlist Authorized Scripts: Use technical controls, such as digital signatures and version control, to ensure that only authorized scripts, such as specific .ps1, .py, etc., files, are allowed to execute. Block unauthorized scripts from executing. Reassess bi-annually, or more frequently.

5. Use intrusion detection signatures to block traffic at network boundaries. (M1031: Network Intrusion Prevention)

• Safeguard 13.3: Deploy a Network Intrusion Detection Solution: Deploy a network intrusion detection solution on enterprise assets, where appropriate. Example implementations include the use of a Network Intrusion Detection System (NIDS) or equivalent cloud service provider (CSP) service.
• Safeguard 13.8: Deploy a Network Intrusion Prevention Solution: Deploy a network intrusion prevention solution, where appropriate. Example implementations include the use of a Network Intrusion Prevention System (NIPS) or equivalent CSP service.

REFERENCES:

Mozilla:
https://www.mozilla.org/en-US/security/advisories/mfsa2023-27/

CVE:
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-3417
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-3600

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