CVE-1999-1010 in OpenSSH
Summary
by MITRE
An SSH 1.2.27 server allows a client to use the "none" cipher, even if it is not allowed by the server policy.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-1010 represents a significant security flaw in SSH protocol implementation that emerged during the early stages of secure remote access adoption. This issue affects SSH server versions including 1.2.27 and demonstrates a critical misconfiguration in cipher selection policies that undermines the fundamental security assurances provided by the SSH protocol. The vulnerability specifically relates to the server's inability to properly enforce its configured cipher policies, creating a potential attack vector that could be exploited by malicious actors seeking to compromise secure connections.
The technical flaw manifests when an SSH server configured to reject certain cipher types, particularly the "none" cipher, fails to properly validate client requests. The "none" cipher in SSH represents a null encryption method that provides no actual cryptographic protection, essentially allowing data to be transmitted in plaintext form. When a server permits clients to negotiate the use of this cipher despite explicit policy restrictions, it creates a dangerous scenario where attackers can downgrade security measures and potentially intercept sensitive information. This behavior violates fundamental principles of secure communication protocols and represents a clear deviation from expected security policy enforcement mechanisms.
From an operational impact perspective, this vulnerability significantly weakens the security posture of systems relying on SSH for remote access and file transfers. The ability to bypass cipher restrictions means that even organizations implementing strict security policies around encryption strength can have their protections undermined. Attackers exploiting this vulnerability could potentially perform man-in-the-middle attacks, capture credentials, or intercept confidential data transmitted over SSH connections. The impact extends beyond simple data theft to encompass potential system compromise and unauthorized access to sensitive infrastructure components. This vulnerability particularly affects environments where strict cryptographic standards are required, such as government agencies, financial institutions, and healthcare organizations that must comply with regulatory requirements for data protection.
The security implications of this vulnerability align with CWE-310, which addresses cryptographic weaknesses in protocol implementations, and represents a clear violation of the principle of least privilege in security policy enforcement. Organizations should implement immediate mitigations including updating SSH server implementations to properly enforce cipher policies, configuring servers to explicitly disable the "none" cipher, and conducting comprehensive security audits of existing SSH deployments. Additionally, this vulnerability highlights the importance of proper security testing and validation of cryptographic implementations, as outlined in the NIST SP 800-57 standard for cryptographic key management and protocol security. System administrators should also consider implementing network monitoring solutions to detect unauthorized cipher negotiation attempts and establish incident response procedures to address potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper security policy enforcement in cryptographic systems and the necessity of thorough testing of security controls before deployment in production environments.