CVE-2005-2771 in SSH server
Summary
by MITRE
WRQ Reflection for Secure IT Windows Server 6.0 (formerly known as F-Secure SSH server) processes access and deny lists in a case-sensitive manner, when previous versions were case-insensitive, which might allow remote attackers to bypass intended restrictions and login to accounts that should be denied.
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Analysis
by VulDB Data Team • 07/19/2024
The vulnerability identified as CVE-2005-2771 affects WRQ Reflection for Secure IT Windows Server 6.0, formerly known as the F-Secure SSH server, presenting a significant security regression in access control implementation. This issue represents a critical deviation from established security practices where the software transitioned from case-insensitive to case-sensitive processing of access and deny lists, fundamentally altering the security posture of the system.
The technical flaw manifests in the server's handling of user authentication lists where previously case-insensitive matching allowed for more flexible access control. The change to case-sensitive processing creates a scenario where attackers can exploit the difference in string comparison behavior to bypass intended security restrictions. When access and deny lists contain usernames or group names with different case variations, the case-sensitive approach fails to properly match against the intended restrictions, potentially allowing unauthorized access to accounts that should be denied access.
This vulnerability directly impacts the authentication and authorization mechanisms of the SSH server, creating a path for remote attackers to gain access to systems that should be protected. The operational impact extends beyond simple unauthorized access as it undermines the principle of least privilege and can lead to privilege escalation scenarios where attackers might gain access to accounts with elevated permissions. The vulnerability is particularly dangerous because it operates silently, with attackers not necessarily being detected during the unauthorized access attempts.
The security implications of this vulnerability align with CWE-284, which addresses improper access control, and represents a regression in security configuration management. Attackers can exploit this by carefully crafting usernames with specific case variations that would bypass the deny lists, effectively circumventing the intended access restrictions. The vulnerability also relates to ATT&CK technique T1078 which covers valid accounts and privilege escalation through legitimate access mechanisms.
Mitigation strategies should focus on immediate patching of the affected software to restore the previous case-insensitive behavior or implementing additional access control measures such as network segmentation, firewall rules, and monitoring for unusual authentication patterns. Organizations should also review their existing access control policies to ensure proper enforcement of case-sensitive versus case-insensitive matching across all authentication systems. Additionally, implementing comprehensive logging and monitoring of authentication attempts can help detect exploitation attempts and provide evidence for forensic analysis.
The vulnerability demonstrates the critical importance of maintaining consistent security behaviors across software updates and the potential for seemingly minor implementation changes to create significant security weaknesses. Organizations should conduct thorough security testing when implementing updates to authentication systems and ensure that any changes to access control behavior are carefully evaluated for potential security regressions. Regular security audits of authentication mechanisms and access control lists should be performed to identify and remediate similar issues that might exist in other systems within the network infrastructure.