CVE-2018-6553 in Linux
Summary
by MITRE
The CUPS AppArmor profile incorrectly confined the dnssd backend due to use of hard links. A local attacker could possibly use this issue to escape confinement. This flaw affects versions prior to 2.2.7-1ubuntu2.1 in Ubuntu 18.04 LTS, prior to 2.2.4-7ubuntu3.1 in Ubuntu 17.10, prior to 2.1.3-4ubuntu0.5 in Ubuntu 16.04 LTS, and prior to 1.7.2-0ubuntu1.10 in Ubuntu 14.04 LTS.
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Analysis
by VulDB Data Team • 05/01/2023
The vulnerability described in CVE-2018-6553 represents a critical confinement bypass issue within the Common Unix Printing System CUPS implementation on Ubuntu systems. This flaw specifically targets the AppArmor security framework's ability to properly contain the dnssd backend process, which is responsible for DNS service discovery functionality within the printing subsystem. The vulnerability stems from improper handling of hard links within the AppArmor profile configuration, creating a pathway for local attackers to potentially escape the intended security boundaries. The issue affects multiple Ubuntu LTS versions including 14.04, 16.04, 17.10, and 18.04, demonstrating the widespread impact across different system generations. According to CWE-257, this represents a weakness in the security policy enforcement mechanism where the system fails to properly restrict access to resources that should be confined within specific boundaries. The vulnerability directly relates to the AppArmor security model's failure to prevent privilege escalation through hard link manipulation.
The technical exploitation of this vulnerability relies on the attacker's ability to manipulate hard links within the CUPS system configuration, specifically targeting the dnssd backend process that handles DNS service discovery for printer discovery. When the AppArmor profile incorrectly handles hard links, it fails to properly restrict the backend's access to system resources that should be isolated. This misconfiguration allows a local attacker to potentially access files, directories, or processes that should be restricted by the security profile. The flaw operates at the kernel level where hard link resolution bypasses the intended confinement mechanisms, creating a path for privilege escalation and information disclosure. The attack vector requires local system access, making it a local privilege escalation vulnerability that could potentially allow an attacker to gain elevated privileges or access sensitive system information. This vulnerability aligns with ATT&CK technique T1068 which covers privilege escalation through the exploitation of system vulnerabilities.
The operational impact of CVE-2018-6553 extends beyond simple confinement bypass as it affects the fundamental security architecture of the printing subsystem on affected Ubuntu systems. A successful exploitation could allow local attackers to access printer configuration data, network discovery information, or potentially escalate privileges to gain root access on the system. The vulnerability particularly impacts enterprise environments where CUPS is widely deployed for printer management, as it could enable attackers to gain unauthorized access to sensitive network information or system resources. Organizations running affected Ubuntu versions face potential exposure to local privilege escalation attacks that could compromise the integrity of their printing infrastructure. The vulnerability's presence in multiple LTS versions indicates that many organizations may be running exposed systems for extended periods without proper patching, creating prolonged attack windows. System administrators should consider this vulnerability in their risk assessment frameworks as it represents a persistent security gap in the system's ability to maintain proper process isolation. The remediation process requires updating the CUPS package to versions that properly handle hard links within the AppArmor profile, ensuring that the security boundaries remain intact. Organizations should implement comprehensive patch management procedures to address this vulnerability and prevent potential exploitation through local privilege escalation attacks.