CVE-2016-6636 in Cloud Foundry
Summary
by MITRE
The OAuth authorization implementation in Pivotal Cloud Foundry (PCF) before 242; UAA 2.x before 2.7.4.7, 3.x before 3.3.0.5, and 3.4.x before 3.4.4; UAA BOSH before 11.5 and 12.x before 12.5; Elastic Runtime before 1.6.40, 1.7.x before 1.7.21, and 1.8.x before 1.8.1; and Ops Manager 1.7.x before 1.7.13 and 1.8.x before 1.8.1 mishandles redirect_uri subdomains, which allows remote attackers to obtain implicit access tokens via a modified subdomain.
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Analysis
by VulDB Data Team • 04/28/2019
The vulnerability described in CVE-2016-6636 represents a critical flaw in the OAuth authorization implementation within Pivotal Cloud Foundry ecosystems, specifically affecting multiple versions of the User Account and Authentication (UAA) service and related components. This weakness stems from improper handling of redirect_uri parameters during OAuth flows, creating a significant security gap that could be exploited by remote attackers to gain unauthorized access to user sessions and sensitive authentication tokens.
The technical flaw manifests in the insufficient validation of redirect_uri subdomain handling within the OAuth authorization process. When applications attempt to redirect users back to specific subdomains after authentication, the system fails to properly verify that the redirect target remains within the expected domain boundaries. This allows attackers to manipulate the redirect_uri parameter to point to malicious subdomains that they control, thereby enabling them to capture implicit access tokens that should only be accessible to legitimate applications. The vulnerability specifically impacts the OAuth 2.0 implicit grant flow where access tokens are returned directly to the client without an intermediate authorization code, making the attack surface particularly dangerous.
The operational impact of this vulnerability extends across multiple Pivotal Cloud Foundry components and versions, creating widespread exposure for organizations using affected releases of PCF, UAA, Elastic Runtime, and Ops Manager. Attackers leveraging this flaw can obtain implicit access tokens without proper authorization, potentially gaining access to user accounts, applications, and underlying infrastructure resources. This capability significantly undermines the security model of the platform, as it allows unauthorized parties to impersonate legitimate users and access protected resources within the cloud environment. The vulnerability affects both the authentication and authorization mechanisms, potentially leading to data breaches, privilege escalation, and unauthorized access to cloud resources.
Organizations affected by this vulnerability should prioritize immediate remediation through patching all affected versions of Pivotal Cloud Foundry components, specifically upgrading UAA to versions 2.7.4.7, 3.3.0.5, or 3.4.4, and ensuring all related components are updated to their secure releases. The mitigation strategy should include implementing strict redirect_uri validation rules that enforce domain boundary checking and prevent subdomain manipulation. Security teams should also conduct comprehensive assessments of their OAuth implementations to identify similar vulnerabilities and implement proper input validation mechanisms. This vulnerability aligns with CWE-601 and CWE-200, representing URL redirection issues and information exposure respectively, and maps to ATT&CK techniques involving credential access and privilege escalation through authentication manipulation. Organizations should also consider implementing additional monitoring and logging of OAuth flows to detect potential exploitation attempts and establish proper security controls around redirect_uri parameter handling.