CVE-2016-2047 in MySQL Server
Summary
by MITRE
The ssl_verify_server_cert function in sql-common/client.c in MariaDB before 5.5.47, 10.0.x before 10.0.23, and 10.1.x before 10.1.10; Oracle MySQL 5.5.48 and earlier, 5.6.29 and earlier, and 5.7.11 and earlier; and Percona Server do not properly verify that the server hostname matches a domain name in the subject's Common Name (CN) or subjectAltName field of the X.509 certificate, which allows man-in-the-middle attackers to spoof SSL servers via a "/CN=" string in a field in a certificate, as demonstrated by "/OU=/CN=bar.com/CN=foo.com."
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Analysis
by VulDB Data Team • 07/26/2022
The vulnerability described in CVE-2016-2047 represents a critical flaw in SSL certificate verification mechanisms within several major database systems including MariaDB, Oracle MySQL, and Percona Server. This issue stems from improper implementation of hostname validation during SSL/TLS certificate verification processes, creating a significant security gap that adversaries can exploit to conduct man-in-the-middle attacks. The flaw specifically affects versions prior to the patched releases, with MariaDB being vulnerable before 5.5.47, 10.0.23, and 10.1.10, while Oracle MySQL versions 5.5.48, 5.6.29, and 5.7.11 and earlier remain susceptible to this vulnerability.
The technical root cause of this vulnerability lies in the ssl_verify_server_cert function's inadequate validation of X.509 certificate subject fields, particularly the Common Name (CN) and subjectAltName attributes. According to the certificate verification process defined in RFC 5280 and implemented through the OpenSSL library, proper hostname validation should ensure that the server's hostname matches at least one domain name present in either the CN field or the subjectAltName extension of the certificate. However, the affected database systems fail to properly parse and validate these fields, allowing attackers to craft malicious certificates containing multiple CN entries where one of the entries matches the target domain. This vulnerability specifically exploits the fact that when multiple CN values exist in a certificate, the verification process does not properly validate all entries against the expected hostname.
The operational impact of this vulnerability is severe and directly enables sophisticated man-in-the-middle attacks where attackers can impersonate legitimate database servers. The demonstration example shows how an attacker could create a certificate with "/CN=bar.com/CN=foo.com" where one of the CN entries matches the target database server's domain name, allowing successful certificate validation despite the certificate being malicious. This flaw essentially bypasses the fundamental security principle of certificate-based authentication, making it possible for attackers to intercept and potentially modify database communications without detection. The vulnerability is particularly dangerous in environments where database connections are authenticated using SSL/TLS, as it undermines the entire security infrastructure built around certificate verification.
This vulnerability maps directly to CWE-295, which specifically addresses "Improper Certificate Validation," and aligns with several ATT&CK techniques including T1566 for credential access through phishing and T1046 for network service scanning. The attack vector typically involves an attacker positioned between the client and server, intercepting database connections and presenting a maliciously crafted certificate that passes the flawed validation checks. Organizations using affected database versions face significant risk of data exfiltration, database manipulation, and unauthorized access to sensitive information stored within these systems. The vulnerability also demonstrates the importance of proper certificate validation implementation as outlined in NIST SP 800-57 and ISO/IEC 15408 standards for cryptographic module validation.
Mitigation strategies for this vulnerability require immediate patching of affected database versions to the latest secure releases from vendors. Organizations should also implement additional network security controls including firewall rules to restrict database access, network segmentation to limit exposure, and monitoring of SSL/TLS handshake failures. The recommended approach includes deploying certificate pinning mechanisms, implementing strict certificate validation policies, and conducting regular security assessments of database configurations. System administrators should also consider implementing network-based intrusion detection systems to monitor for suspicious certificate validation patterns and ensure that all database connections utilize properly configured and validated certificates from trusted certificate authorities. Additionally, organizations should review their certificate management practices to ensure proper validation of certificate chains and implement automated monitoring for certificate expiration and potential security issues.