CVE-2019-19519 in OpenBSD
Summary
by MITRE
In OpenBSD 6.6, local users can use the su -L option to achieve any login class (often excluding root) because there is a logic error in the main function in su/su.c.
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Analysis
by VulDB Data Team • 03/07/2024
The vulnerability identified as CVE-2019-19519 represents a critical privilege escalation flaw within the OpenBSD operating system's su command implementation. This issue affects OpenBSD version 6.6 and allows local attackers to bypass normal authentication restrictions by exploiting a logic error in the command's main function. The su command, which is fundamental to Unix-like systems for switching user identities, becomes compromised when users employ the -L option, enabling them to assume any login class except root. This flaw fundamentally undermines the security model of the operating system by allowing unauthorized privilege elevation without proper authentication mechanisms.
The technical root cause of this vulnerability lies in a logic error within the main function of the su/su.c source file, specifically in how the program handles login class validation when the -L option is specified. The flaw demonstrates characteristics consistent with CWE-284, which addresses improper access control, and CWE-250, relating to execution with unnecessary privileges. When the su command processes the -L option, it fails to properly validate or enforce the restrictions that should prevent users from assuming arbitrary login classes. This logic error creates a pathway where legitimate users can manipulate the command to bypass the normal class-based access controls that typically prevent privilege escalation.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with the ability to assume various user roles within the system's security framework. Since the vulnerability specifically excludes root access, it represents a partial but significant compromise of the system's access control model. Attackers can leverage this flaw to gain access to resources and capabilities typically restricted to specific login classes, potentially enabling further exploitation or data access. The implications are particularly severe in multi-user environments where different login classes are used to enforce security boundaries and limit user capabilities. This vulnerability affects the fundamental security architecture of OpenBSD by undermining the principle of least privilege and creating potential entry points for more sophisticated attacks.
Mitigation strategies for this vulnerability require immediate patching of the OpenBSD system to the corrected version that addresses the logic error in su/su.c. System administrators should prioritize applying the official security update from OpenBSD to resolve the flaw at the source. Additionally, organizations should implement monitoring for unauthorized use of the su command with the -L option and review existing user permissions to minimize potential exploitation opportunities. The remediation process should include verifying that all systems have been updated and conducting security audits to ensure no unauthorized privilege escalation has occurred. This vulnerability serves as a reminder of the critical importance of maintaining up-to-date system software and the potential consequences of logic errors in core system utilities that handle privilege management. The flaw also highlights the need for rigorous code review processes and security testing of authentication mechanisms, particularly those that form the foundation of system security models.