CVE-2012-5975 in SSH Server
Summary
by MITRE
The SSH USERAUTH CHANGE REQUEST feature in SSH Tectia Server 6.0.4 through 6.0.20, 6.1.0 through 6.1.12, 6.2.0 through 6.2.5, and 6.3.0 through 6.3.2 on UNIX and Linux, when old-style password authentication is enabled, allows remote attackers to bypass authentication via a crafted session involving entry of blank passwords, as demonstrated by a root login session from a modified OpenSSH client with an added input_userauth_passwd_changereq call in sshconnect2.c.
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Analysis
by VulDB Data Team • 12/29/2024
The vulnerability described in CVE-2012-5975 represents a critical authentication bypass flaw within SSH Tectia Server versions spanning multiple release branches from 6.0.4 through 6.3.2 on UNIX and Linux platforms. This issue specifically targets the SSH USERAUTH CHANGE REQUEST functionality that handles password authentication processes. The flaw manifests when old-style password authentication is enabled, creating a pathway for remote attackers to circumvent the standard authentication mechanisms through carefully crafted session sequences. The vulnerability was demonstrated through a modified OpenSSH client implementation that introduced an additional input_userauth_passwd_changereq call within the sshconnect2.c source file, enabling attackers to exploit the authentication flow during root login sessions.
The technical root cause of this vulnerability stems from improper handling of password change requests within the SSH authentication process. When the server encounters a password change request, it fails to properly validate whether the authentication attempt should proceed normally or if it should be treated as a password change operation. This misconfiguration allows attackers to submit blank password inputs during the authentication phase, effectively bypassing the need for valid credentials. The flaw is particularly dangerous because it operates at the protocol level where authentication decisions are made, allowing unauthorized access to privileged accounts. The vulnerability is classified under CWE-287, which addresses improper handling of authentication credentials, and aligns with ATT&CK technique T1078.101 for valid accounts and T1566 for phishing attacks that can exploit authentication bypasses.
The operational impact of this vulnerability is severe and far-reaching, particularly in environments where SSH Tectia Server is deployed for remote administrative access. An attacker exploiting this vulnerability could gain unauthorized root access to systems, potentially leading to complete system compromise and data exfiltration. The vulnerability affects not only individual servers but also entire network infrastructures where SSH is used for administrative access, as it allows for lateral movement and privilege escalation. The attack vector requires only remote access to the affected SSH service, making it particularly dangerous in publicly accessible environments. Organizations using affected versions of SSH Tectia Server face significant risk of unauthorized access to critical systems, especially when root login sessions are permitted.
Mitigation strategies for CVE-2012-5975 must include immediate patching of affected SSH Tectia Server installations to versions that address the authentication bypass vulnerability. Organizations should disable old-style password authentication where possible and implement alternative authentication methods such as public key authentication or multi-factor authentication. Network segmentation and access controls should be enhanced to limit exposure of affected systems, while monitoring should be implemented to detect unusual authentication patterns or unauthorized access attempts. The vulnerability also highlights the importance of maintaining up-to-date security patches and conducting regular vulnerability assessments. Security teams should consider implementing additional controls such as SSH key management systems, automated patch management solutions, and comprehensive monitoring of authentication events to detect and prevent exploitation attempts. Organizations should also review their SSH configuration policies to ensure that unnecessary authentication methods are disabled and that access controls are properly enforced.