CVE-2005-2666 in OpenSSH
Summary
by MITRE
ssh as implemented in openssh before 4.0 and possibly other implementations stores hostnames ip addresses and keys in plaintext in the known_hosts file which makes it easier for an attacker that has compromised an ssh user s account to generate a list of additional targets that are more likely to have the same password or key.
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Analysis
by VulDB Data Team • 06/30/2025
The vulnerability described in CVE-2005-2666 represents a significant security weakness in the OpenSSH implementation that affected versions prior to 4.0. This flaw resides in the handling of host identification and authentication data within the known_hosts file, which serves as a critical component in SSH protocol security. The vulnerability stems from the plaintext storage of sensitive information including hostnames, IP addresses, and cryptographic keys, creating an exploitable condition that undermines the fundamental security model of SSH connections.
The technical implementation of this vulnerability involves the insecure storage practices within the OpenSSH client's known_hosts file management system. When users establish SSH connections to remote hosts, the client automatically records the host's identification information including its hostname, IP address, and public key fingerprint. In versions before 4.0, this information was stored in plain text format without any encryption or obfuscation, making it immediately accessible to any user with read access to the file. This design flaw directly violates security best practices for sensitive data handling and creates a persistent attack surface that can be exploited by malicious actors who have already gained unauthorized access to a user account.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates a pathway for attackers to conduct targeted reconnaissance and credential reuse attacks. When an attacker compromises an SSH user account, they can leverage the information stored in the known_hosts file to identify other systems that the user has previously accessed, potentially revealing additional targets that share similar authentication credentials or key configurations. This information can be particularly valuable for attackers attempting to escalate privileges or move laterally within a network, as it provides a list of systems that are more likely to be vulnerable to the same authentication methods used against the initial target.
The vulnerability aligns with multiple CWE categories including CWE-312 (Sensitive Data Exposure) and CWE-522 (Insufficiently Protected Credentials), as it demonstrates how plaintext storage of authentication-related information creates exploitable conditions. From an ATT&CK framework perspective, this vulnerability enables techniques such as credential access through credential dumping and privilege escalation via lateral movement, as attackers can use the stored information to identify and target additional systems without requiring additional reconnaissance efforts. The weakness also contributes to the broader category of information disclosure attacks that can be used to build comprehensive attack profiles for target systems.
Mitigation strategies for this vulnerability primarily involve upgrading to OpenSSH version 4.0 or later, where the implementation was corrected to address the plaintext storage issue. Organizations should also implement proper file system access controls to limit read access to known_hosts files, ensuring that only authorized users can access this sensitive information. Additional protective measures include regular monitoring of SSH access patterns, implementing strong account access controls, and establishing proper network segmentation to limit the potential impact of credential compromise. The vulnerability serves as a critical reminder of the importance of secure data handling practices and the need for regular security updates to address known weaknesses in cryptographic implementations.