CVE-2015-5889 in Mac OS X
Summary
by MITRE
rsh in the remote_cmds component in Apple OS X before 10.11 allows local users to obtain root privileges via vectors involving environment variables.
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Analysis
by VulDB Data Team • 11/21/2024
The vulnerability identified as CVE-2015-5889 represents a critical privilege escalation flaw within Apple's OS X operating system affecting versions prior to 10.11. This issue specifically resides within the remote_cmds component that includes the rsh (remote shell) utility, which has historically been a source of security concerns due to its inherent design weaknesses and lack of proper authentication mechanisms. The vulnerability exploits a fundamental flaw in how the rsh utility handles environment variables, creating an avenue for local attackers to elevate their privileges from standard user level to root access. The remote_cmds framework was designed to provide remote execution capabilities but suffered from poor security implementation that persisted across multiple OS X releases.
The technical exploitation mechanism involves manipulating environment variables that are passed to the rsh utility during execution. When a local user executes rsh with specific environment variable modifications, the system fails to properly sanitize or validate these variables before they are processed by the privileged component. This creates a path where attacker-controlled variables can influence the execution context of the rsh utility, ultimately allowing arbitrary code execution with root privileges. The flaw demonstrates a classic insecure parameter handling vulnerability where user input directly affects system behavior without adequate validation or isolation. This vulnerability falls under the CWE-78 weakness category, which specifically addresses improper neutralization of special elements used in OS command construction, and aligns with ATT&CK technique T1068 for privilege escalation through local exploitation.
The operational impact of this vulnerability is severe as it enables any local user to gain root access without requiring authentication or additional attack vectors. This represents a fundamental compromise of the system's security model where the boundary between user and system privileges becomes meaningless. Attackers can leverage this vulnerability to install persistent backdoors, modify system files, access sensitive data, or completely compromise the machine's integrity. The vulnerability is particularly dangerous because it requires no network connectivity or external attack surface, making it exploitable through simple local user interaction. The attack vector is straightforward and reliable, making it a preferred target for both malicious actors and penetration testers seeking to establish persistent access to compromised systems.
Mitigation strategies for CVE-2015-5889 primarily involve upgrading to Apple OS X version 10.11 or later where the vulnerability has been addressed through improved environment variable handling and privilege separation mechanisms. System administrators should disable the rsh service entirely if it is not required for legacy applications, as the utility itself is considered deprecated and insecure. Additional protective measures include implementing proper access controls and monitoring for unusual environment variable modifications, though these are secondary to the primary mitigation of system updates. The vulnerability serves as a reminder of the importance of proper privilege separation and input validation in system components, particularly those that handle user-provided data in contexts that can affect system-level operations. Organizations should also conduct comprehensive security assessments to identify any remaining instances of deprecated remote execution utilities that may present similar vulnerabilities.