CVE-2002-0755 in FreeBSD
Summary
by MITRE
Kerberos 5 su (k5su) in FreeBSD 4.5 and earlier does not verify that a user is a member of the wheel group before granting superuser privileges, which could allow unauthorized users to execute commands as root.
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Analysis
by VulDB Data Team • 02/11/2017
The vulnerability identified as CVE-2002-0755 represents a critical authorization flaw in the Kerberos 5 su implementation within FreeBSD operating systems version 4.5 and earlier. This issue specifically affects the k5su utility which serves as a Kerberos-aware version of the standard su command, designed to facilitate secure privilege escalation using Kerberos authentication mechanisms. The flaw stems from inadequate group membership verification during the privilege escalation process, creating a significant security weakness that undermines the fundamental principle of least privilege in Unix-like systems.
The technical nature of this vulnerability resides in the improper validation of user credentials within the Kerberos authentication framework. When users attempt to escalate privileges using k5su, the system fails to confirm whether the authenticated user belongs to the privileged wheel group, which traditionally controls administrative access to the system. This omission allows any user who can successfully authenticate through Kerberos to execute commands with root privileges, regardless of their actual administrative status or authorization level. The vulnerability essentially bypasses the group-based access control mechanisms that form the cornerstone of Unix security models, creating an unauthorized privilege escalation vector.
The operational impact of CVE-2002-0755 extends beyond simple unauthorized access, as it fundamentally compromises the integrity of the system's privilege management architecture. An attacker exploiting this vulnerability can execute arbitrary commands with root privileges, potentially leading to complete system compromise, data exfiltration, or persistent backdoor installation. This flaw particularly affects environments where Kerberos authentication is deployed for administrative access, as it renders the entire authentication framework ineffective for privilege control. The vulnerability also impacts the principle of defense in depth, as it bypasses multiple security layers including authentication, authorization, and access control mechanisms that should normally prevent unauthorized privilege escalation.
From a cybersecurity perspective, this vulnerability aligns with CWE-284, which addresses improper access control issues in software systems. The flaw represents a classic case of insufficient authorization checking where the system fails to properly validate user credentials against established security policies. This vulnerability also maps to ATT&CK technique T1068, which covers privilege escalation through the use of system tools, specifically targeting the exploitation of legitimate administrative tools to gain unauthorized access. Organizations running affected FreeBSD versions face significant risk of compromise, as this vulnerability can be exploited remotely without requiring additional attack vectors beyond successful Kerberos authentication.
Mitigation strategies for CVE-2002-0755 require immediate system updates to FreeBSD versions that address the group membership verification issue. Administrators should ensure that all affected systems are patched promptly, as the vulnerability remains exploitable for extended periods. Additional compensating controls include implementing strict network segmentation to limit access to Kerberos services, monitoring authentication logs for unusual privilege escalation attempts, and reviewing user access controls to ensure that only authorized personnel have Kerberos credentials. Security teams should also consider implementing multi-factor authentication for Kerberos services and establishing robust audit trails to detect potential exploitation attempts. The vulnerability highlights the critical importance of proper access control implementation and the necessity of thorough security testing for authentication and authorization mechanisms within operating system components.