CVE-2023-27561 is a vulnerability in the runc container runtime, specifically affecting versions up to 1.1.4. The issue is an incorrect access control flaw in the libcontainer/rootfs_linux.go component, which leads to escalation of privileges on the host system. This vulnerability is a regression from a previously known issue (CVE-2019-19921), indicating that a prior fix was undone or insufficiently addressed. To exploit this vulnerability, an attacker must have the ability to spawn two containers with custom volume-mount configurations and run custom container images. This means the attacker needs some level of access to the container environment but does not require full administrative privileges on the host. The vulnerability allows the attacker to escape container isolation and gain elevated privileges on the host, potentially compromising the entire system. The CVSS v3.1 base score is 7.0 (High), with vector AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H, indicating local attack vector, high attack complexity, low privileges required, no user interaction, unchanged scope, and high impact on confidentiality, integrity, and availability. No public exploits have been reported yet, but the risk remains significant due to the nature of containerized environments and the widespread use of runc as a container runtime component in Docker, Kubernetes, and other platforms. The vulnerability highlights the importance of secure container configuration, especially regarding volume mounts and image trust. Organizations relying on container technology should monitor for patches and apply them promptly to prevent potential host compromise.

For European organizations, the impact of CVE-2023-27561 can be substantial, especially for those heavily utilizing containerized environments in cloud-native applications, microservices, and DevOps pipelines. Successful exploitation allows an attacker with limited container privileges to escalate to host-level privileges, potentially leading to full system compromise. This can result in unauthorized access to sensitive data, disruption of critical services, and lateral movement within networks. Given the increasing adoption of container orchestration platforms like Kubernetes, which rely on runc as the default runtime, the vulnerability poses a risk to cloud service providers, financial institutions, healthcare providers, and government agencies in Europe. The breach of container isolation undermines the security model of containerization, increasing the attack surface. Additionally, the vulnerability could be leveraged in multi-tenant environments or shared infrastructure, amplifying the potential damage. The absence of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as attackers often reverse-engineer patches to develop exploits. Therefore, the vulnerability demands urgent attention to prevent exploitation and maintain trust in container security.

1. Update runc to the latest patched version as soon as it becomes available from trusted sources or vendor distributions. 2. Restrict container creation permissions to trusted users only, minimizing the ability of unprivileged users to spawn containers with custom configurations. 3. Enforce strict image provenance policies by using signed and verified container images to prevent running untrusted or malicious images. 4. Limit or audit volume mount configurations in containers, especially those that allow mounting host directories, to reduce the risk of container escape via filesystem manipulation. 5. Implement runtime security monitoring and anomaly detection tools that can identify suspicious container behavior or privilege escalation attempts. 6. Use container security frameworks and policies (e.g., Pod Security Policies, Open Policy Agent) to enforce least privilege and secure container configurations. 7. Regularly audit container runtime versions and configurations as part of vulnerability management programs. 8. Educate DevOps and security teams about the risks of container escape vulnerabilities and best practices for secure container deployment. 9. Consider isolating critical workloads in dedicated environments with additional security controls to limit blast radius if exploitation occurs.