CVE-2019-3814 in Dovecot
Summary
by MITRE
It was discovered that Dovecot before versions 2.2.36.1 and 2.3.4.1 incorrectly handled client certificates. A remote attacker in possession of a valid certificate with an empty username field could possibly use this issue to impersonate other users.
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Analysis
by VulDB Data Team • 08/17/2023
The vulnerability identified as CVE-2019-3814 affects Dovecot email server implementations prior to versions 2.2.36.1 and 2.3.4.1, representing a critical authentication flaw that undermines the security of certificate-based user identification mechanisms. This issue stems from improper handling of client certificates within the authentication process, creating a potential pathway for unauthorized access and privilege escalation. The flaw specifically manifests when a remote attacker possesses a valid certificate that contains an empty username field, enabling them to exploit the certificate validation logic and impersonate legitimate users within the system.
The technical root cause of this vulnerability lies in Dovecot's insufficient validation of certificate attributes during the authentication handshake process. When client certificates are presented to the server, the system should rigorously verify all identifying fields including usernames, distinguished names, and certificate authorities. However, the flawed implementation fails to properly enforce validation checks on certificates with empty username fields, allowing attackers to manipulate the authentication flow. This represents a classic case of inadequate input validation and authentication control, aligning with CWE-285 which addresses authentication bypass issues. The vulnerability essentially creates a condition where certificate-based authentication becomes ineffective, as the system cannot reliably distinguish between legitimate and malicious certificate presentations.
The operational impact of this vulnerability extends beyond simple unauthorized access, potentially enabling attackers to gain elevated privileges and access sensitive email data belonging to other users. An attacker with a valid certificate and an empty username field can exploit this flaw to traverse user boundaries within the email system, potentially accessing confidential communications, personal information, and business data. This type of privilege escalation attack directly violates the principle of least privilege and can lead to significant data breaches and privacy violations. The vulnerability affects organizations relying on certificate-based authentication for secure email access, particularly those implementing secure email protocols such as IMAP and POP3 with TLS client certificate authentication.
Security professionals should prioritize immediate remediation of this vulnerability by upgrading Dovecot installations to versions 2.2.36.1 or 2.3.4.1, which contain the necessary patches to address the certificate handling flaw. Organizations should also implement additional monitoring to detect unusual authentication patterns that might indicate exploitation attempts. The mitigation strategy should include comprehensive review of certificate management policies and enforcement of strict certificate validation procedures. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and credential access methods, specifically targeting the T1078 credential access sub-technique related to valid accounts and T1550 use of legitimate credentials. Organizations should conduct thorough security assessments to identify all systems utilizing vulnerable Dovecot versions and ensure proper certificate lifecycle management to prevent similar issues in the future.