CVE-2016-0800 in NonStop BackBox
Summary
by MITRE
The SSLv2 protocol, as used in OpenSSL before 1.0.1s and 1.0.2 before 1.0.2g and other products, requires a server to send a ServerVerify message before establishing that a client possesses certain plaintext RSA data, which makes it easier for remote attackers to decrypt TLS ciphertext data by leveraging a Bleichenbacher RSA padding oracle, aka a "DROWN" attack.
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Analysis
by VulDB Data Team • 01/27/2025
The vulnerability described in CVE-2016-0800 represents a critical weakness in the SSLv2 protocol implementation that has profound implications for cryptographic security. This flaw specifically affects OpenSSL versions prior to 1.0.1s and 1.0.2g, as well as other software products that implement SSLv2. The vulnerability stems from the protocol's design where servers must send a ServerVerify message before confirming that clients possess specific plaintext RSA data, creating a fundamental security gap that adversaries can exploit.
The technical mechanism behind this vulnerability operates through a sophisticated cryptographic attack vector known as the Bleichenbacher RSA padding oracle. When SSLv2 is enabled on a server, it creates an environment where attackers can perform a series of carefully crafted requests to determine whether a particular RSA decryption operation will succeed. This oracle allows adversaries to gradually recover plaintext data from encrypted TLS ciphertext through a process of iterative guessing and validation, effectively breaking the encryption layer that should protect sensitive communications. The attack leverages the fact that the SSLv2 protocol's handshake process does not properly validate client credentials before proceeding with cryptographic operations, creating a window of opportunity for exploitation.
The operational impact of this vulnerability is severe and far-reaching, particularly in environments where SSLv2 remains enabled for backward compatibility reasons. Attackers can leverage this weakness to decrypt sensitive TLS traffic, potentially accessing confidential information such as login credentials, personal data, financial transactions, and proprietary communications. The DROWN attack specifically targets the RSA encryption mechanism and can be executed remotely without requiring authentication, making it particularly dangerous for web servers, email servers, and other network services that may still support legacy SSLv2 connections. This vulnerability undermines the fundamental security assumptions of TLS encryption, as it allows attackers to bypass the intended cryptographic protections through a flaw in the protocol's design rather than through direct cryptographic weaknesses.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security posture improvements. The primary recommendation involves disabling SSLv2 support entirely on all systems, as the protocol is fundamentally flawed and should not be used in production environments. Organizations should update their OpenSSL implementations to versions 1.0.1s or 1.0.2g and later, which contain patches addressing this specific vulnerability. Additionally, security teams should conduct comprehensive audits to identify any remaining SSLv2 implementations across their infrastructure, including legacy applications that may have been configured to support the protocol for compatibility reasons. Network administrators should also implement proper monitoring to detect any attempts to establish SSLv2 connections, as these may indicate potential exploitation attempts or misconfigurations that could be leveraged by attackers.
This vulnerability aligns with CWE-310, which addresses cryptographic weaknesses in key management and implementation, and represents a classic example of how legacy protocol support can create security vulnerabilities that persist long after their original design flaws have been identified. The attack pattern corresponds to techniques described in the MITRE ATT&CK framework under credential access and defense evasion tactics, as it allows attackers to bypass encryption protections and access credentials or sensitive data without detection. The DROWN attack demonstrates the importance of maintaining up-to-date cryptographic implementations and the dangers of supporting deprecated protocols that may contain inherent design flaws that can be exploited by determined attackers. Organizations should also consider implementing automated security scanning tools that can detect SSLv2 usage and alert administrators to potential exposure risks, as this vulnerability can remain undetected for extended periods if not properly monitored.