CVE-2017-6507 in AppArmor
Summary
by MITRE
An issue was discovered in AppArmor before 2.12. Incorrect handling of unknown AppArmor profiles in AppArmor init scripts, upstart jobs, and/or systemd unit files allows an attacker to possibly have increased attack surfaces of processes that were intended to be confined by AppArmor. This is due to the common logic to handle 'restart' operations removing AppArmor profiles that aren't found in the typical filesystem locations, such as /etc/apparmor.d/. Userspace projects that manage their own AppArmor profiles in atypical directories, such as what's done by LXD and Docker, are affected by this flaw in the AppArmor init script logic.
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Analysis
by VulDB Data Team • 08/25/2024
The vulnerability identified as CVE-2017-6507 represents a critical flaw in AppArmor's profile handling mechanism that undermines the security isolation intended by the mandatory access control system. This issue affects AppArmor versions prior to 2.12 and stems from improper logic in the initialization scripts that manage AppArmor profile loading and restart operations. The flaw occurs when the system attempts to restart AppArmor services and encounters profiles that are not located in the standard filesystem paths, particularly the conventional /etc/apparmor.d/ directory where profiles are typically stored. When these profiles cannot be located, the system's default behavior is to remove them from the active configuration, inadvertently creating a security gap that allows processes to run without proper confinement.
The technical root cause of this vulnerability lies in the flawed restart logic that operates under the assumption that all AppArmor profiles must reside in predictable locations. This design decision creates a dangerous precedent where the system's attempt to clean up or reset configurations actually weakens security by removing legitimate profiles that exist in non-standard locations. The vulnerability specifically impacts how AppArmor handles profile persistence during service restarts, where the system fails to properly account for profiles managed by third-party applications or containerization platforms. This behavior creates an attack surface where processes that should remain confined can escape their intended security boundaries, potentially allowing privilege escalation or information disclosure attacks.
The operational impact of this vulnerability extends beyond simple profile removal, as it fundamentally undermines the security model that AppArmor is designed to enforce. When containerization platforms like LXD and Docker manage their own AppArmor profiles in custom directories, these profiles become vulnerable to being stripped away during system restarts or service management operations. This creates a persistent security weakness where the very mechanism designed to protect system resources becomes a vector for bypassing confinement controls. The vulnerability affects upstart jobs and systemd unit files, meaning that any service management approach used by the system can potentially trigger this flaw, making it particularly dangerous in enterprise environments where automated service management is common. The issue is categorized under CWE-225, which addresses improper handling of exceptional conditions, specifically in the context of security configuration management.
Security implications of CVE-2017-6507 align with several ATT&CK techniques including privilege escalation through service management manipulation and defense evasion via configuration modification. Attackers can exploit this vulnerability by placing malicious or misconfigured profiles in non-standard locations, then triggering a system restart or service reload operation that causes the legitimate profiles to be removed, thereby weakening the overall security posture. The flaw particularly affects containerized environments where LXD and Docker implementations rely on custom profile locations, making it a significant concern for cloud and virtualization deployments. Organizations using AppArmor for system hardening may find their security controls effectively neutralized through this seemingly benign restart operation, creating a false sense of security while actually exposing systems to unauthorized access. The vulnerability demonstrates the critical importance of proper configuration management in security systems and highlights how automated cleanup operations can inadvertently create security holes when they fail to account for legitimate custom deployments.
Mitigation strategies for this vulnerability require immediate patching of AppArmor to version 2.12 or later where the flawed restart logic has been corrected. System administrators should also implement strict profile location policies to prevent the use of non-standard directories for AppArmor profiles, though this approach may not be feasible in containerized environments. Organizations should conduct thorough audits of their AppArmor profile deployments to identify any custom locations that may be vulnerable to this flaw. Additionally, implementing monitoring for unauthorized profile modifications and service restart operations can help detect exploitation attempts. The fix addresses the core issue by ensuring that profiles in non-standard locations are properly preserved during restart operations, maintaining the intended confinement boundaries that AppArmor is designed to enforce. Regular security assessments should include verification that AppArmor profiles remain active and properly configured after system updates and service management operations to prevent this vulnerability from compromising security controls.