CVE-2016-0704 in Integrated Lights Out Manager
Summary
by MITRE
An oracle protection mechanism in the get_client_master_key function in s2_srvr.c in the SSLv2 implementation in OpenSSL before 0.9.8zf, 1.0.0 before 1.0.0r, 1.0.1 before 1.0.1m, and 1.0.2 before 1.0.2a overwrites incorrect MASTER-KEY bytes during use of export cipher suites, which makes it easier for remote attackers to decrypt TLS ciphertext data by leveraging a Bleichenbacher RSA padding oracle, a related issue to CVE-2016-0800.
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Analysis
by VulDB Data Team • 02/02/2023
The vulnerability described in CVE-2016-0704 represents a critical flaw in OpenSSL's SSLv2 implementation that specifically affects the handling of master key material during export cipher suite operations. This issue manifests in the get_client_master_key function within s2_srvr.c, where an oracle protection mechanism fails to properly handle incorrect MASTER-KEY bytes, creating a significant security weakness that can be exploited by remote attackers to compromise encrypted communications. The vulnerability is particularly concerning because it directly relates to cryptographic oracle attacks, which have been extensively documented in cybersecurity literature and represent a well-known class of attacks that can undermine the security of encrypted communications.
The technical flaw in this vulnerability stems from the improper handling of cryptographic key material during the SSLv2 handshake process, specifically when export cipher suites are being utilized. During the SSLv2 protocol negotiation, when export cipher suites are selected, the system should properly validate and handle the master key bytes to prevent information leakage. However, the flawed implementation in OpenSSL overwrites incorrect MASTER-KEY bytes in a manner that creates a timing or response-based oracle that can be exploited by attackers. This behavior directly maps to CWE-310, which addresses cryptographic weaknesses in key management and oracle-based attacks. The vulnerability is particularly dangerous because it enables attackers to perform Bleichenbacher RSA padding oracle attacks, where the attacker can iteratively determine the plaintext by analyzing the responses from the cryptographic oracle, ultimately leading to the decryption of TLS ciphertext data.
The operational impact of CVE-2016-0704 extends far beyond simple cryptographic weakness, as it fundamentally undermines the confidentiality guarantees that TLS encryption is designed to provide. Remote attackers who can successfully exploit this vulnerability can decrypt sensitive data transmitted over TLS connections, potentially accessing confidential information such as login credentials, personal data, financial information, and proprietary business data. The attack vector is particularly insidious because it requires no local access or authentication, making it a significant threat to web applications, email systems, and any service that relies on SSLv2 or vulnerable TLS implementations. This vulnerability directly aligns with ATT&CK technique T1566, which covers credential access through the exploitation of cryptographic vulnerabilities, and T1071, which addresses application layer protocol manipulation through the exploitation of encryption weaknesses.
The remediation strategy for CVE-2016-0704 requires immediate deployment of patched OpenSSL versions that address the specific issue in the get_client_master_key function. Organizations should upgrade to OpenSSL versions 0.9.8zf, 1.0.0r, 1.0.1m, or 1.0.2a, which contain the necessary fixes to prevent the improper overwriting of MASTER-KEY bytes during export cipher suite operations. Beyond patching, system administrators should disable SSLv2 support entirely, as this protocol version is fundamentally insecure and has been deprecated for years due to numerous cryptographic weaknesses. The vulnerability also highlights the importance of proper cryptographic implementation practices and the need for thorough testing of oracle protection mechanisms. Security teams should implement monitoring for any unusual cryptographic behavior or timing variations that might indicate exploitation attempts, and should conduct regular vulnerability assessments to identify any remaining instances of SSLv2 usage within their infrastructure. This vulnerability serves as a critical reminder of the importance of proper key management and the dangers of implementing cryptographic systems without adequate consideration of oracle-based attack vectors that can be leveraged by sophisticated adversaries.