CVE-2001-1029 in OpenSSH
Summary
by MITRE
libutil in OpenSSH on FreeBSD 4.4 and earlier does not drop privileges before verifying the capabilities for reading the copyright and welcome files, which allows local users to bypass the capabilities checks and read arbitrary files by specifying alternate copyright or welcome files.
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Analysis
by VulDB Data Team • 08/16/2024
The vulnerability described in CVE-2001-1029 represents a critical privilege escalation issue within the OpenSSH implementation on FreeBSD systems. This flaw exists in the libutil library component of OpenSSH versions running on FreeBSD 4.4 and earlier releases. The core problem lies in the improper sequence of operations during the SSH daemon initialization process where privilege dropping occurs after capability verification rather than before it. This design flaw creates a window of opportunity for local attackers to exploit the system's security controls. The vulnerability specifically affects the handling of copyright and welcome files that are typically used during SSH session establishment. When an attacker specifies alternate copyright or welcome files, the system performs capability checks against these files before dropping privileges from root to a lower-privileged user account. This temporal mismatch allows malicious users to bypass the intended access controls and read arbitrary files on the system that would normally be restricted to root access.
The technical exploitation of this vulnerability follows a specific attack pattern that leverages the improper privilege management sequence. During SSH daemon startup, the system first validates the capabilities of specified copyright and welcome files without having dropped root privileges. This validation process checks file permissions and access controls, but since the process is still running as root, it can bypass normal file system restrictions. An attacker can create malicious symbolic links or specify alternate file paths that point to sensitive system files such as /etc/shadow, /etc/passwd, or other restricted resources. The vulnerability is particularly dangerous because it operates at the system level where the SSH daemon typically runs with elevated privileges, and the privilege dropping mechanism fails to occur at the appropriate time. This flaw directly violates security principle of least privilege and demonstrates poor implementation of privilege management within the OpenSSH codebase.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks. Local users who can access the system can exploit this flaw to read sensitive system files that contain authentication credentials, system configurations, and other confidential information. The ability to bypass capability checks means that attackers can access files that are normally protected by the operating system's file permission model. This vulnerability essentially allows privilege escalation from a local user account to a level where sensitive system resources become accessible. The attack requires local system access but does not require network connectivity or remote exploitation, making it particularly concerning for systems where local access is possible. The implications include potential credential theft, system reconnaissance, and the ability to gather information that could be used for further attacks within the network infrastructure.
Mitigation strategies for CVE-2001-1029 must address the fundamental flaw in privilege management within the OpenSSH implementation. The most effective approach involves upgrading to FreeBSD versions that contain patched OpenSSH implementations where the privilege dropping mechanism occurs before capability verification. System administrators should also implement strict file access controls and monitor for unauthorized changes to SSH configuration files. The vulnerability aligns with CWE-250, which describes "Execute Code with Unnecessary Privileges," and demonstrates how improper privilege management can lead to unauthorized access. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques where attackers leverage implementation flaws to gain elevated system access. Additional defensive measures include implementing mandatory access controls, regular system auditing, and ensuring that SSH daemon configurations do not allow arbitrary file specification. The patch for this vulnerability specifically addresses the sequence of operations in the libutil library to ensure that privilege dropping occurs before any file access validation, thereby preventing the exploitation window that enables this attack vector.