CVE-2016-0896 in Cloud Foundry Elastic Runtime
Summary
by MITRE
Pivotal Cloud Foundry (PCF) Elastic Runtime before 1.6.34 and 1.7.x before 1.7.12 places 169.254.0.0/16 in the all_open Application Security Group, which might allow remote attackers to bypass intended network-connectivity restrictions by leveraging access to the 169.254.169.254 address.
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Analysis
by VulDB Data Team • 04/18/2019
The vulnerability identified as CVE-2016-0896 affects Pivotal Cloud Foundry Elastic Runtime versions prior to 1.6.34 and 1.7.x versions before 1.7.12, representing a significant network security flaw that undermines the intended isolation mechanisms of cloud applications. This issue stems from the improper configuration of Application Security Groups (ASGs) within the PCF platform, specifically involving the inclusion of the 169.254.0.0/16 network range in the all_open ASG. The 169.254.0.0/16 subnet is a link-local addressing range defined in RFC 3927, commonly used for automatic private IP address allocation and typically restricted to local network communication. When this subnet is inadvertently opened to all applications through the all_open ASG, it creates a critical security gap that allows unauthorized network access.
The technical flaw manifests through the misconfiguration of network security policies within the PCF platform's security group management system. Application Security Groups function as network access control lists that define which network traffic is allowed to reach applications running on the platform. The all_open ASG, designed to provide maximum network access for testing or development environments, should not include link-local addresses that are explicitly reserved for local network operations. The inclusion of 169.254.0.0/16 in this unrestricted group creates a pathway for remote attackers to exploit the platform's network connectivity by leveraging the 169.254.169.254 address, which is a well-known endpoint used for cloud instance metadata services. This metadata endpoint typically provides sensitive information about the virtual machine instance, including instance IDs, network configuration details, and potentially credential information that could be used for further exploitation.
The operational impact of this vulnerability extends beyond simple network access bypass, creating a potential gateway for more sophisticated attacks within cloud environments. Attackers could leverage this flaw to conduct reconnaissance activities, gather instance metadata, or potentially perform lateral movement within the cloud infrastructure. The vulnerability particularly affects organizations using PCF for production deployments where network isolation and security boundaries are critical for protecting sensitive applications and data. The implications are significant because cloud platforms like PCF are designed to provide secure multi-tenant environments where applications should be isolated from each other, and this flaw undermines those fundamental security assumptions. The vulnerability also demonstrates poor security configuration management practices within the platform's default security policies, suggesting that organizations may be exposed to similar issues in other network security configurations.
Organizations should implement immediate mitigations including updating to the patched versions of PCF Elastic Runtime 1.6.34 and 1.7.12, which properly exclude the 169.254.0.0/16 subnet from the all_open ASG. Additionally, security teams should conduct thorough audits of their Application Security Group configurations to ensure no other reserved or link-local address ranges are inadvertently included in unrestricted groups. The remediation process should involve reviewing and restricting all ASG configurations to only include necessary network ranges, implementing network segmentation policies, and establishing automated monitoring for unauthorized changes to security group configurations. This vulnerability aligns with CWE-284, which describes improper access control, and maps to ATT&CK techniques related to network service scanning and privilege escalation through network access control bypass. Organizations should also consider implementing network traffic monitoring and anomaly detection systems to identify potential exploitation attempts targeting link-local addresses or metadata services within their cloud environments.