CVE-2019-8337 in msmtp
Summary
by MITRE
In msmtp 1.8.2, when tls_trust_file has its default configuration, certificate-verification results are not properly checked.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 07/10/2023
The vulnerability identified as CVE-2019-8337 affects the msmtp email client version 1.8.2, specifically within its Transport Layer Security implementation. This flaw resides in the default configuration handling of the tls_trust_file parameter, which is critical for establishing secure email communications. The issue stems from improper certificate verification procedures when the system operates with default settings, creating a potential security gap that could be exploited by malicious actors. The msmtp utility is commonly used for sending emails from command-line interfaces and automated scripts, making this vulnerability particularly concerning for system administrators and security practitioners who rely on secure email transmission mechanisms.
The technical flaw manifests when the tls_trust_file parameter is left at its default configuration, which typically points to a system-wide certificate store or uses default trust anchors. Under normal circumstances, proper certificate verification should validate the authenticity and integrity of TLS certificates presented by email servers during the secure connection establishment process. However, in this vulnerable state, the verification checks are bypassed or inadequately performed, allowing potentially malicious or untrusted certificates to be accepted as valid. This represents a fundamental breakdown in the cryptographic security model that msmtp relies upon for secure email communications. The vulnerability falls under CWE-295 which specifically addresses improper certificate validation, and aligns with ATT&CK technique T1566 related to credential harvesting through phishing or similar means.
The operational impact of this vulnerability extends beyond simple email delivery failures, as it fundamentally undermines the security posture of systems relying on msmtp for secure communications. Attackers could exploit this weakness by presenting forged certificates to intercept or modify email traffic, potentially gaining access to sensitive information or compromising the integrity of email communications. Systems using default msmtp configurations without proper certificate validation could become entry points for man-in-the-middle attacks, particularly in environments where email security is paramount such as financial institutions, healthcare organizations, or government agencies. The vulnerability is especially dangerous in automated environments where email notifications are critical for system monitoring, security alerts, or business processes, as compromised email channels could lead to undetected security breaches or operational disruptions.
Mitigation strategies for CVE-2019-8337 should begin with immediate configuration updates to ensure that tls_trust_file points to a properly maintained and secure certificate authority store. System administrators should verify that certificate validation is explicitly enabled and properly configured rather than relying on default settings that may be insecure. The recommended approach involves implementing explicit certificate validation controls and maintaining up-to-date certificate trust stores that align with industry best practices for TLS security. Organizations should also consider implementing monitoring solutions to detect potential certificate validation failures or unauthorized certificate changes in their email infrastructure. Regular security audits of email client configurations and automated certificate validation processes can help identify and remediate similar vulnerabilities. Additionally, upgrading to patched versions of msmtp that address this specific certificate validation issue should be prioritized as part of comprehensive vulnerability management programs. The vulnerability highlights the critical importance of proper cryptographic configuration and the necessity of avoiding default security settings that may be insufficient for production environments.