CVE-2015-3627 in Libcontainer
Summary
by MITRE
Libcontainer and Docker Engine before 1.6.1 opens the file-descriptor passed to the pid-1 process before performing the chroot, which allows local users to gain privileges via a symlink attack in an image.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 05/17/2022
The vulnerability identified as CVE-2015-3627 represents a critical privilege escalation flaw affecting libcontainer and Docker Engine versions prior to 1.6.1. This issue stems from improper handling of file descriptors during container initialization processes, specifically within the context of process isolation and system security boundaries. The flaw manifests when the container runtime environment fails to properly secure file descriptor access before executing the chroot system call, creating a window of opportunity for malicious actors to exploit the system.
The technical implementation of this vulnerability involves a race condition or improper privilege management during container startup procedures. When Docker creates a container, it initializes a pid-1 process that typically executes within the container's isolated environment. However, in affected versions, the system opens file descriptors before performing the chroot operation, which changes the root directory for the process. This sequence allows local users to manipulate symbolic links in the container image, effectively creating a symlink attack vector that can be exploited to gain elevated privileges. The flaw is particularly dangerous because it operates at the kernel level where privilege separation is critical for maintaining system security boundaries.
The operational impact of CVE-2015-3627 extends beyond simple privilege escalation, as it fundamentally undermines the security model of containerized environments. Attackers can leverage this vulnerability to execute arbitrary code with root privileges on the host system, potentially compromising the entire infrastructure. This represents a significant breach of container isolation principles where the security boundary between host and container becomes porous. The vulnerability affects organizations using Docker containers for application deployment, making it particularly concerning for cloud environments, continuous integration systems, and microservices architectures that rely heavily on containerization technologies.
Mitigation strategies for this vulnerability require immediate patching of affected Docker Engine versions to 1.6.1 or later, which implements proper file descriptor handling before chroot operations. Organizations should also implement additional security measures including regular vulnerability scanning of container images, monitoring for suspicious symlink creation, and implementing least privilege principles for container execution. The fix addresses the underlying CWE-276 vulnerability category related to incorrect permissions and improper privilege management, aligning with ATT&CK technique T1068 which covers privilege escalation through local exploitation. Security teams should also consider implementing container runtime security solutions that can detect and prevent symlink attacks, as well as establishing robust image validation processes to prevent malicious content from entering containerized environments.