CVE-1999-0720 in Linux
Summary
by MITRE
The pt_chown command in Linux allows local users to modify TTY terminal devices that belong to other users.
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Analysis
by VulDB Data Team • 09/25/2024
The vulnerability described in CVE-1999-0720 represents a significant privilege escalation issue within early Linux systems, specifically targeting the pt_chown utility that manages ownership of pseudo-terminal devices. This flaw exists in the permission handling mechanisms of terminal device management, where the pt_chown command fails to properly validate user permissions when modifying TTY terminal device ownership. The vulnerability stems from inadequate access control checks that allow local users to manipulate terminal devices owned by other system users, effectively bypassing the intended security boundaries that should protect user isolation within the operating system.
The technical implementation of this vulnerability resides in the pt_chown command's failure to properly verify whether the requesting user has legitimate authorization to modify the ownership of specific terminal devices. This represents a classic case of insufficient privilege checking and improper access control enforcement, which can be categorized under CWE-284 - Improper Access Control. The flaw operates at the system call level where terminal device ownership transitions occur without proper validation of the initiating user's privileges, allowing malicious local users to exploit this weakness to gain unauthorized access to terminal sessions and potentially escalate their privileges to higher levels within the system.
From an operational impact perspective, this vulnerability creates a substantial security risk for local users who can leverage this weakness to compromise the integrity of terminal sessions belonging to other users. Attackers can use this privilege escalation vector to access sensitive information, monitor communications, or potentially execute commands in contexts where they should not have access. The vulnerability particularly affects multi-user environments where different users share the same system, as it undermines the fundamental security principle of user isolation. This weakness can be exploited to gain unauthorized access to terminal sessions, potentially leading to information disclosure, system compromise, or further privilege escalation attacks. The impact is further amplified in environments where users have different security contexts or where terminal sessions contain sensitive data or administrative access.
The mitigation strategies for CVE-1999-0720 should focus on implementing proper access control mechanisms within the pt_chown command and ensuring that all terminal device ownership modifications require appropriate authorization checks. System administrators should ensure that the pt_chown utility properly validates user credentials and permissions before allowing ownership changes to occur. This vulnerability aligns with ATT&CK technique T1068 - Exploitation for Privilege Escalation, where attackers leverage system weaknesses to gain higher privileges. The recommended approach involves updating system software packages to versions that properly implement access controls, implementing proper user authentication checks, and ensuring that terminal device ownership changes require explicit authorization from the system administrator. Additionally, monitoring and logging of terminal device ownership changes should be implemented to detect potential exploitation attempts. Organizations should also consider implementing mandatory access controls and privilege separation mechanisms to prevent unauthorized access to terminal devices, as this vulnerability represents a fundamental failure in the system's privilege management architecture that can be exploited to undermine the entire security model of the operating system.