CVE-2015-3631 in Docker
Summary
by MITRE
Docker Engine before 1.6.1 allows local users to set arbitrary Linux Security Modules (LSM) and docker_t policies via an image that allows volumes to override files in /proc.
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Analysis
by VulDB Data Team • 05/17/2022
The vulnerability identified as CVE-2015-3631 represents a critical privilege escalation flaw in Docker Engine versions prior to 1.6.1 that stems from improper handling of Linux Security Modules and volume mount operations. This issue enables local attackers to manipulate the security policies of the host system by leveraging the ability of containerized applications to override files within the /proc filesystem through volume mappings. The vulnerability specifically exploits the interaction between Docker's volume management system and the Linux kernel's security framework, creating a pathway for malicious actors to elevate their privileges and potentially compromise the entire host environment.
The technical flaw manifests through Docker's volume mounting mechanism which, in affected versions, fails to properly validate or restrict the ability of containers to map host directories into their filesystem hierarchy. When a container is configured with volume mounts that include directories within /proc, the Docker engine does not adequately enforce security boundaries that would normally prevent such mappings. This allows an attacker to place a malicious image containing specific volume configurations that can override critical files in the /proc directory, particularly those related to security module configurations. The vulnerability is particularly dangerous because it operates at the kernel level, where the Linux Security Module framework (LSM) policies are enforced, enabling attackers to inject arbitrary security policies that can bypass normal access controls.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential full system compromise and persistent access. An attacker who successfully exploits this vulnerability can manipulate the security policies that govern how the Linux kernel enforces access controls, potentially allowing them to disable security features or grant themselves elevated privileges that persist beyond the container lifecycle. This represents a significant threat to containerized environments where multiple users or applications share the same host system, as the vulnerability can be exploited to gain root access to the underlying host machine. The attack vector is particularly concerning because it requires minimal privileges to initiate and can be executed through standard Docker image creation and deployment processes.
Mitigation strategies for CVE-2015-3631 primarily focus on updating to Docker Engine version 1.6.1 or later, which includes fixes that properly enforce security boundaries when handling volume mounts. Organizations should also implement strict container image validation policies that prevent the use of images with potentially dangerous volume mount configurations. Network segmentation and privilege separation practices should be reinforced to limit the potential impact of successful exploitation. The vulnerability aligns with CWE-276, which addresses improper privilege management, and maps to ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation'. System administrators should also consider implementing additional monitoring for unusual volume mount operations and filesystem changes within /proc directories, as these activities may indicate attempted exploitation of this vulnerability. Regular security audits of container configurations and image repositories are essential to prevent deployment of potentially malicious containers that could exploit this flaw.