CVE-2011-4318 in Dovecot
Summary
by MITRE
Dovecot 2.0.x before 2.0.16, when ssl or starttls is enabled and hostname is used to define the proxy destination, does not verify that the server hostname matches a domain name in the subject s Common Name (CN) of the X.509 certificate, which allows man-in-the-middle attackers to spoof SSL servers via a valid certificate for a different hostname.
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Analysis
by VulDB Data Team • 12/29/2021
The vulnerability identified as CVE-2011-4318 affects Dovecot email server software versions 2.0.x prior to 2.0.16, specifically when SSL or STARTTLS encryption is enabled with hostname-based proxy configurations. This represents a critical security flaw that undermines the fundamental trust model of SSL/TLS communications by failing to properly validate certificate subject names against the expected server hostname. The issue arises from inadequate certificate validation logic that only examines the Common Name field without considering the broader certificate subject alternative name extensions that modern SSL implementations should utilize for comprehensive hostname verification.
The technical flaw stems from Dovecot's insufficient implementation of hostname verification during SSL/TLS handshakes when proxy configurations rely on hostname resolution. When a client connects to a Dovecot server configured with ssl or starttls and hostname-based proxy destinations, the server accepts certificates that contain valid X.509 certificates but for different hostnames than what the client expects. This vulnerability falls under CWE-295, which specifically addresses improper certificate validation, and more broadly relates to CWE-310, concerning cryptographic issues. The flaw allows attackers to perform man-in-the-middle attacks by presenting a legitimate certificate for one hostname while the client expects a different hostname, effectively bypassing the SSL certificate validation mechanism that should prevent such impersonation attacks.
The operational impact of this vulnerability is severe as it enables attackers to intercept and potentially modify email communications without detection. In a typical email server environment, this vulnerability could allow malicious actors to eavesdrop on email exchanges, steal authentication credentials, or even modify email content during transmission. The vulnerability is particularly dangerous in corporate environments where Dovecot serves as an email server, as it could compromise sensitive business communications and potentially lead to data breaches or credential theft. The attack vector is relatively simple to exploit since attackers only need to obtain a valid SSL certificate for a different hostname and position themselves between the client and server to intercept communications.
Mitigation strategies for CVE-2011-4318 primarily involve upgrading to Dovecot version 2.0.16 or later, which contains the necessary certificate validation fixes. Organizations should also implement comprehensive certificate management policies that ensure SSL certificates are properly validated against expected hostnames and consider deploying additional security controls such as certificate pinning where appropriate. The fix implemented in Dovecot 2.0.16 addresses the core issue by enforcing stricter hostname validation that checks not only the Common Name field but also the Subject Alternative Name extensions in X.509 certificates, aligning with best practices recommended by the ATT&CK framework for network security and certificate validation. Additionally, administrators should conduct regular security assessments of their email infrastructure and ensure that all SSL/TLS configurations follow industry standards including proper certificate validation procedures and monitoring for potential certificate mismatches.