CVE-2017-4970 in Cloud Foundry
Summary
by MITRE
An issue was discovered in Cloud Foundry Foundation cf-release v255 and Staticfile buildpack versions v1.4.0 - v1.4.3. A regression introduced in the Static file build pack causes the Staticfile.auth configuration to be ignored when the Static file file is not present in the application root. Applications containing a Staticfile.auth file but not a Static file had their basic auth turned off when an operator upgraded the Static file build pack in the foundation to one of the vulnerable versions. Note that Static file applications without a Static file are technically misconfigured, and will not successfully detect unless the Static file build pack is explicitly specified.
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Analysis
by VulDB Data Team • 10/16/2019
The vulnerability described in CVE-2017-4970 represents a critical configuration regression within the Cloud Foundry Staticfile buildpack ecosystem that fundamentally undermines authentication security for web applications. This issue specifically affects Cloud Foundry Foundation cf-release version 255 and Staticfile buildpack versions ranging from v1.4.0 through v1.4.3, creating a scenario where legitimate security controls are silently disabled without operator awareness. The flaw manifests when applications contain a Staticfile.auth configuration file but lack the expected Staticfile in the application root directory, which is a common deployment pattern for applications that rely solely on authentication mechanisms without requiring static file serving.
The technical root cause of this vulnerability stems from a regression in the buildpack's parsing logic that fails to properly evaluate authentication configurations when the expected static file component is absent from the application directory structure. This regression creates a logical error in the buildpack's decision-making process where it incorrectly determines that basic authentication should be disabled when the Staticfile is not present, regardless of the explicit Staticfile.auth configuration that operators have provided. The vulnerability operates at the configuration management layer and represents a clear violation of the principle of least privilege, as it allows unauthorized access to applications that were explicitly configured to require authentication. This behavior directly aligns with CWE-284 Access Control Issues, specifically manifesting as improper access control due to incorrect configuration handling.
The operational impact of this vulnerability is particularly severe for organizations relying on Cloud Foundry deployments where basic authentication serves as a primary security control for protecting sensitive applications. When operators upgrade the Staticfile buildpack to vulnerable versions, they unknowingly disable authentication mechanisms that were explicitly configured by application developers or security teams. This regression essentially creates a security blind spot where applications that should be protected by basic authentication become publicly accessible, potentially exposing sensitive data, internal APIs, or administrative interfaces. The vulnerability is especially concerning because it operates silently without generating error messages or alerts, making it difficult to detect through normal monitoring procedures. This silent failure pattern increases the risk of prolonged exposure and aligns with ATT&CK technique T1566 Credential Access through Social Engineering, as the vulnerability creates opportunities for unauthorized access that bypass legitimate security controls.
Organizations affected by this vulnerability should immediately implement mitigation strategies to restore proper authentication controls. The primary remediation involves either downgrading to a non-vulnerable buildpack version or ensuring that all applications containing Staticfile.auth configurations also include a properly configured Staticfile in the root directory. Additionally, operators should conduct comprehensive audits of their Cloud Foundry deployments to identify applications that may have been affected by this regression, particularly those that rely exclusively on authentication mechanisms without static file serving. Security teams should also implement enhanced monitoring for authentication configuration changes and establish automated checks to verify that basic authentication remains properly enabled for applications that require it. The vulnerability highlights the importance of thorough regression testing for buildpack updates and demonstrates the critical need for configuration validation mechanisms that prevent silent security control failures. Organizations should also consider implementing more robust deployment pipelines that include security validation steps before applying buildpack updates to production environments, ensuring that authentication controls remain intact during infrastructure modifications.