CVE-2004-0009 in Apache-SSL
Summary
by MITRE
Apache-SSL 1.3.28+1.52 and earlier, with SSLVerifyClient set to 1 or 3 and SSLFakeBasicAuth enabled, allows remote attackers to forge a client certificate by using basic authentication with the "one-line DN" of the target user.
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Analysis
by VulDB Data Team • 05/20/2019
This vulnerability exists in Apache-SSL versions 1.3.28 and earlier, specifically when the SSLVerifyClient directive is configured with values of 1 or 3, combined with SSLFakeBasicAuth enabled. The flaw stems from a critical design oversight in how the server handles client authentication when fake basic authentication is active. When SSLVerifyClient is set to 1 or 3, the server typically requires valid client certificates for authentication, but the interaction with SSLFakeBasicAuth creates an exploitable condition where attackers can bypass proper certificate validation.
The technical mechanism of exploitation involves leveraging the basic authentication mechanism to forge client certificate identities. Attackers can construct a "one-line DN" representation of a target user's certificate and use it within basic authentication headers. This approach exploits a weakness in the certificate verification process where the server accepts the forged identity without proper validation of the actual certificate chain. The vulnerability represents a classic case of inadequate input validation and authentication bypass, classified under CWE-287 which addresses improper authentication mechanisms.
The operational impact of this vulnerability is significant as it allows remote attackers to impersonate legitimate users within the SSL-secured environment. This creates a pathway for unauthorized access to protected resources, potentially leading to data breaches, privilege escalation, and complete system compromise. The vulnerability affects organizations relying on Apache-SSL for secure web services where client certificate authentication is enforced but the server configuration inadvertently enables this attack vector. This weakness directly maps to ATT&CK technique T1550.001 which covers use of valid credentials, and T1071.001 which involves application layer protocol usage.
Organizations should immediately disable SSLFakeBasicAuth when SSLVerifyClient is set to 1 or 3, or alternatively, upgrade to Apache-SSL versions beyond 1.52 where this vulnerability has been addressed. The recommended mitigation strategy involves reconfiguring the SSL server to either disable fake basic authentication entirely or ensure that when enabled, it does not interfere with certificate verification processes. Additionally, implementing proper certificate validation controls and monitoring for suspicious authentication patterns can help detect exploitation attempts. The vulnerability highlights the importance of proper security configuration management and the principle of least privilege in SSL/TLS implementations, where enabling features that weaken authentication mechanisms can create severe security implications.