CVE-2020-5416 in Cloud Foundry Routing
Summary
by MITRE
Cloud Foundry Routing (Gorouter), versions prior to 0.204.0, when used in a deployment with NGINX reverse proxies in front of the Gorouters, is potentially vulnerable to denial-of-service attacks in which an unauthenticated malicious attacker can send specially-crafted HTTP requests that may cause the Gorouters to be dropped from the NGINX backend pool.
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Analysis
by VulDB Data Team • 11/10/2020
The vulnerability identified as CVE-2020-5416 affects Cloud Foundry Routing components, specifically the Gorouter service, which serves as a critical ingress point for applications deployed within Cloud Foundry environments. This issue manifests when Gorouters operate in conjunction with NGINX reverse proxies, creating a potential attack surface that adversaries can exploit to disrupt service availability. The vulnerability stems from improper handling of specific HTTP request patterns that can trigger unexpected behavior in the routing layer, ultimately leading to service degradation or complete unavailability of routing functionality.
The technical flaw resides in how the Gorouter processes certain HTTP requests when deployed behind NGINX proxies. Attackers can craft malicious HTTP requests that cause the Gorouter to become unresponsive or to fail health checks that NGINX uses to determine backend availability. This occurs due to insufficient input validation and improper error handling within the routing component, allowing specially crafted requests to trigger internal state changes that result in the router being removed from the NGINX backend pool. The vulnerability is particularly concerning because it requires no authentication, making it accessible to any external attacker with network access to the affected deployment.
The operational impact of this vulnerability extends beyond simple service disruption, as it can lead to cascading failures within Cloud Foundry deployments. When Gorouters are removed from NGINX backend pools, legitimate traffic cannot be properly routed to applications, resulting in complete service outages for affected applications. This vulnerability particularly affects deployments where high availability and continuous service delivery are critical, as the denial-of-service condition can persist until manual intervention occurs or until the affected components are restarted. The attack vector is straightforward and can be automated, making it particularly dangerous in environments where multiple applications depend on the routing infrastructure.
Organizations should implement immediate mitigations by upgrading to Gorouter version 0.204.0 or later, which contains the necessary patches to address the HTTP request handling behavior that enables this attack. Additionally, network-level protections such as rate limiting and request filtering should be implemented at the NGINX level to prevent malicious requests from reaching the vulnerable Gorouter components. The vulnerability aligns with CWE-400, which covers improper handling of input that can lead to denial-of-service conditions, and maps to ATT&CK technique T1499.004 for network disruption attacks. Security teams should also consider implementing monitoring solutions that can detect unusual patterns in routing behavior or sudden increases in health check failures that might indicate exploitation attempts.