CVE-2018-1256 in Spring Cloud SSO Connector
Summary
by MITRE
Spring Cloud SSO Connector, version 2.1.2, contains a regression which disables issuer validation in resource servers that are not bound to the SSO service. In PCF deployments with multiple SSO service plans, a remote attacker can authenticate to unbound resource servers which use this version of the SSO Connector with tokens generated from another service plan.
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Analysis
by VulDB Data Team • 02/02/2020
The vulnerability identified as CVE-2018-1256 affects Spring Cloud Single Sign-On Connector version 2.1.2, specifically impacting resource servers that operate outside the direct binding to the SSO service. This regression represents a critical security flaw in the authentication mechanism that undermines the fundamental security model of multi-tenant cloud deployments. The issue manifests when resource servers are not directly bound to the SSO service, creating a scenario where the system fails to properly validate the token issuer, thereby allowing unauthorized access through token manipulation.
This vulnerability stems from a regression in the SSO Connector's validation logic that was introduced in version 2.1.2, specifically targeting the issuer validation process within resource server configurations. The flaw operates by bypassing the normal validation checks that should ensure tokens originate from the correct SSO service plan, effectively disabling a crucial security control mechanism. According to CWE-287, this represents an authentication vulnerability where improper validation of authentication tokens allows unauthorized users to impersonate legitimate entities within the system.
The operational impact of this vulnerability in PCF (Pivotal Cloud Foundry) deployments with multiple SSO service plans is particularly severe as it enables cross-service token manipulation. A remote attacker can exploit this weakness to authenticate to resource servers that are not bound to the SSO service they are attempting to impersonate, using tokens generated from a different service plan. This creates a lateral movement vector that allows attackers to access resources they should not have authorization to reach, effectively breaking the isolation boundaries between different SSO service plans within the same deployment.
The implications extend beyond simple unauthorized access, as this vulnerability can be leveraged to escalate privileges and move laterally within the cloud environment. Attackers can potentially access sensitive data, modify system configurations, or disrupt services by authenticating through unbound resource servers using tokens from other service plans. This scenario directly aligns with ATT&CK technique T1078.004 which covers valid accounts and T1566 which covers credential harvesting through social engineering or system exploitation.
Organizations using Spring Cloud SSO Connector version 2.1.2 should immediately implement mitigations including upgrading to a patched version of the connector, implementing additional access controls, and monitoring for unauthorized authentication attempts. The recommended approach involves ensuring that all resource servers properly validate issuer information and that appropriate binding relationships are enforced between SSO services and resource servers. Additionally, organizations should consider implementing network segmentation and monitoring solutions to detect anomalous authentication patterns that may indicate exploitation of this vulnerability. The vulnerability demonstrates the importance of maintaining proper authentication boundaries and validating all security controls in multi-tenant cloud environments where service isolation is critical for overall security posture.