CVE-2005-2969 in Serv-U FTP Server
Summary
by MITRE
The SSL/TLS server implementation in OpenSSL 0.9.7 before 0.9.7h and 0.9.8 before 0.9.8a, when using the SSL_OP_MSIE_SSLV2_RSA_PADDING option, disables a verification step that is required for preventing protocol version rollback attacks, which allows remote attackers to force a client and server to use a weaker protocol than needed via a man-in-the-middle attack.
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Analysis
by VulDB Data Team • 07/05/2019
The vulnerability described in CVE-2005-2969 represents a critical weakness in the OpenSSL cryptographic library that specifically affects versions prior to 0.9.7h and 0.9.8a. This flaw occurs within the SSL/TLS server implementation when the SSL_OP_MSIE_SSLV2_RSA_PADDING option is enabled, creating a security gap that fundamentally undermines the integrity of the protocol negotiation process. The vulnerability is particularly concerning because it directly impacts the security of encrypted communications by weakening the protocol version selection mechanism that should prevent downgrade attacks.
The technical flaw stems from the improper handling of protocol version verification when the MSIE_SSLV2_RSA_PADDING option is activated. This option was designed to maintain compatibility with older Microsoft Internet Explorer implementations that used SSL 2.0 padding mechanisms, but it inadvertently disabled a crucial verification step in the SSL/TLS handshake process. Specifically, the implementation fails to properly validate that the negotiated protocol version matches the expected security parameters, creating an opportunity for attackers to manipulate the protocol version selection. This weakness operates at the core of the SSL/TLS protocol stack where version negotiation should enforce security policies rather than allowing arbitrary version selection.
The operational impact of this vulnerability is severe and exploitable through man-in-the-middle attacks that can force both client and server to negotiate a weaker protocol version than what is actually supported. Attackers can leverage this flaw to downgrade connections from TLS 1.0 or higher to SSL 2.0 or other less secure protocols, effectively bypassing modern cryptographic protections. The vulnerability specifically targets the protocol version rollback attack vector, which is a well-documented threat category that has been recognized in various security frameworks including the CWE database under CWE-327, which deals with use of a broken or weak cryptographic algorithm. This weakness creates a direct path for attackers to compromise the security of encrypted communications by forcing the use of weaker cryptographic protocols that are more susceptible to various attacks.
The security implications extend beyond simple protocol downgrade attacks, as this vulnerability can enable more sophisticated attacks that exploit the weaknesses inherent in older SSL protocols. The flaw creates a persistent security gap that affects any system using affected OpenSSL versions with the specific padding option enabled, making it particularly dangerous for web servers, email servers, and any system requiring secure TLS communications. Organizations using vulnerable OpenSSL implementations face significant risk of data interception and compromise, as the vulnerability allows attackers to effectively bypass the security measures that should protect against protocol version downgrade attacks.
Mitigation strategies for CVE-2005-2969 require immediate patching of OpenSSL implementations to versions 0.9.7h or 0.9.8a and later, which contain the necessary fixes to properly enforce protocol version verification. System administrators should disable the SSL_OP_MSIE_SSLV2_RSA_PADDING option on affected systems and ensure that all SSL/TLS implementations properly validate protocol versions during the handshake process. The fix addresses the fundamental issue by restoring the verification step that was being bypassed, thereby preventing attackers from forcing protocol version downgrades. Additionally, organizations should conduct comprehensive audits of their SSL/TLS implementations to identify any other potential vulnerabilities related to protocol version handling and cryptographic protocol enforcement. This vulnerability serves as a prime example of how legacy compatibility features can introduce critical security weaknesses and demonstrates the importance of proper cryptographic protocol implementation in accordance with security best practices established in frameworks such as NIST SP 800-52 and the OWASP Top Ten security risks.