CVE-2007-2768 in OpenSSH
Summary
by MITRE
OpenSSH, when using OPIE (One-Time Passwords in Everything) for PAM, allows remote attackers to determine the existence of certain user accounts, which displays a different response if the user account exists and is configured to use one-time passwords (OTP), a similar issue to CVE-2007-2243.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 07/14/2021
The vulnerability described in CVE-2007-2768 affects OpenSSH implementations that utilize OPIE (One-Time Passwords in Everything) for PAM authentication. This security flaw represents a classic account enumeration issue that can be exploited by remote attackers to identify valid user accounts within a system. The vulnerability specifically manifests when OpenSSH processes authentication requests for users configured to use one-time passwords, creating a distinguishable response pattern that reveals account existence to unauthorized parties.
The technical implementation of this vulnerability stems from the way OpenSSH handles authentication responses when processing OPIE-based authentication requests. When a remote attacker sends an authentication request to an OpenSSH server configured with OPIE, the system responds differently based on whether the target user account exists and is properly configured for OTP authentication. This differential response behavior creates a timing or response pattern that can be analyzed by attackers to determine which accounts are valid and configured for one-time password usage, effectively enabling account enumeration attacks.
From an operational impact perspective, this vulnerability significantly weakens the security posture of systems relying on OpenSSH with OPIE authentication. The account enumeration capability allows attackers to build comprehensive lists of valid user accounts within the target environment, which can then be used for subsequent attacks such as password spraying, brute force attempts, or social engineering campaigns. The vulnerability is particularly concerning because it operates at the authentication layer where attackers can gain intelligence about legitimate users without requiring prior access credentials or system compromise.
The security implications of CVE-2007-2768 align with several established threat frameworks and classifications. This vulnerability can be categorized under CWE-200 (Information Exposure) and represents a specific instance of information leakage through response differentiation. From an ATT&CK framework perspective, this issue maps to techniques involving credential access through enumeration and reconnaissance activities, specifically T1078 (Valid Accounts) and T1562.001 (Impair Defenses). The vulnerability also demonstrates characteristics of privilege escalation through authentication bypass mechanisms, as successful account enumeration can lead to more sophisticated attacks against the identified user accounts.
Mitigation strategies for this vulnerability involve multiple layers of defensive measures. The most effective immediate solution is to disable OPIE authentication when it is not strictly required, or to implement proper input validation and consistent response handling across all authentication paths. Organizations should also consider implementing rate limiting and account lockout mechanisms to prevent automated enumeration attempts. Additionally, network-level protections such as firewall rules and intrusion detection systems can help monitor for suspicious authentication patterns that may indicate enumeration attempts. The recommended approach involves configuring OpenSSH to provide consistent authentication responses regardless of account state, ensuring that the system does not inadvertently reveal information about user account existence through authentication failure patterns.