A critical vulnerability known as CVE-2024-39929 has been identified in Exim Mail Server, impacting versions 4.87 to 4.95.1. This vulnerability enables attackers to bypass security filters, posing a significant risk to email communications and the security of over 15 million mail servers globally. Continue reading this Cybersecurity Threat Advisory to learn which steps to take to mitigate your risk.
What is the threat?
The vulnerability is due to improper handling of certain inputs by Exim, allowing specially crafted emails to evade security filters. This flaw can be exploited without requiring any authentication or user interaction, making it highly dangerous. The vulnerability could allow a remote attacker to bypass filename extension-blocking protection measures and deliver executable attachments directly to end-users’ mailboxes. If a user were to download or run one of these malicious files, the system could be compromised.
Why is it noteworthy?
The critical nature of CVE-2024-39929 leads to the potential for severe impact on organizations’ security, operations, and reputation underscores the urgency of addressing this threat promptly.
- Widespread use: The Exim Mail Server has achieved widespread use globally, with over 15 million installations.
- High severity: The vulnerability has a CVSS score of 9.8.
- Security filter bypass: CVE-2024-39929 allows attackers to bypass security filters, leading to further attacks such as phishing, malware distribution, and unauthorized access to sensitive information.
- Remote code execution: The ability to bypass security filters could lead to remote code execution.
- Low complexity, no authentication required: The attack can occur with low complexity and does not require authentication.
- Potential for widespread damage: Compromising an Exim server can lead to significant operational disruptions, data breaches, and financial losses.
- The urgency of mitigation: Take immediate action to patch affected systems and mitigate the risk.
What is the exposure or risk?
The risk involved in CVE-2024-39929 is significant due to the potential for unauthorized access, remote code execution, service disruption, propagation of malicious activity, privilege escalation, and persistent threats. Given the widespread use of Exim Mail Server, addressing this vulnerability promptly is crucial to maintaining the security and integrity of email systems and overall network infrastructure.
What are the recommendations?
Barracuda MSP recommends the following actions to significantly mitigate the risks associated with CVE-2024-39929:
- Update Exim Mail Server to version 4.95.2 or later, which addresses this critical vulnerability.
- Update all software components to their latest versions to prevent exploitation of known vulnerabilities.
- Configure firewalls to restrict access to the Exim server to trusted IP addresses only.
- Isolate the email server from the rest of the network to limit the impact of a potential breach.
- Implement Barracuda XDR’S Email Protection services for email security solutions and filters to detect and block malicious emails.
- Implement Barracuda XDR’s network and email monitoring for signs of unusual or suspicious activity.
- Apply the principle of least privilege to limit the permissions of the Exim process and associated accounts.
- Implement multi-factor authentication for accessing the email server and administrative interfaces to enhance security.
References
For more in-depth information about the recommendations, please visit the following links:
- https://www.bleepingcomputer.com/news/security/critical-exim-bug-bypasses-security-filters-on-15-million-mail-servers/
- https://thehackernews.com/2024/07/critical-exim-mail-server-vulnerability.html
- https://nvd.nist.gov/vuln/detail/CVE-2024-39929
- https://techpreptalks.com/exim-mail-server-security-alert-cve-2024-39929-poses-major-risk/#the-bigger-picture-cybersecurity-awareness
If you have any questions about this Cybersecurity Threat Advisory, please contact Barracuda XDR’s Security Operations Center.
