CVE-2017-2773 in PCF Elastic Runtime
Summary
by MITRE
An issue was discovered in Pivotal PCF Elastic Runtime 1.6.x versions prior to 1.6.60, 1.7.x versions prior to 1.7.41, 1.8.x versions prior to 1.8.23, and 1.9.x versions prior to 1.9.1. Incomplete validation logic in JSON Web Token (JWT) libraries can allow unprivileged attackers to impersonate other users in multiple components included in PCF Elastic Runtime, aka an "Unauthenticated JWT signing algorithm in multiple components" issue.
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Analysis
by VulDB Data Team • 10/16/2019
The vulnerability identified as CVE-2017-2773 represents a critical security flaw in Pivotal PCF Elastic Runtime affecting multiple version ranges including 1.6.x prior to 1.6.60, 1.7.x prior to 1.7.41, 1.8.x prior to 1.8.23, and 1.9.x prior to 1.9.1. This issue stems from incomplete validation logic within the JSON Web Token (JWT) libraries used throughout the platform, creating a significant authentication bypass opportunity that allows unprivileged attackers to impersonate legitimate users. The vulnerability specifically targets the JWT signing algorithm validation process, which is fundamental to maintaining user identity integrity within the platform's security framework. This flaw operates at the core of the platform's authentication mechanisms, potentially enabling attackers to gain unauthorized access to user accounts and associated privileges across multiple components of the PCF Elastic Runtime environment.
The technical root cause of this vulnerability lies in the improper handling of JWT signing algorithms during token validation processes. When JWT tokens are processed, the system should rigorously validate the signing algorithm used to ensure it matches the expected security parameters and that the token has not been tampered with. However, the vulnerable versions of PCF Elastic Runtime failed to implement complete validation logic, allowing attackers to manipulate the signing algorithm field within JWT tokens. This incomplete validation creates a condition where tokens using the 'none' algorithm or other weak signing methods can be accepted as valid, effectively bypassing the entire authentication mechanism. The flaw manifests as a failure to properly enforce algorithm constraints that should prevent the use of insecure or unauthenticated signing approaches, which is a well-documented weakness in JWT implementations and aligns with common security patterns described in CWE-347.
The operational impact of this vulnerability extends across multiple components within the PCF Elastic Runtime platform, creating widespread potential for unauthorized access and privilege escalation. Attackers exploiting this vulnerability can impersonate legitimate users without requiring valid credentials, potentially gaining access to sensitive applications, user data, and system resources that should be restricted to authorized personnel only. The implications are particularly severe because the vulnerability affects core authentication components that are integral to the platform's security architecture, meaning that a successful exploitation could compromise the entire user access control system. This issue represents a significant threat to the confidentiality, integrity, and availability of services running on the platform, as unauthorized users could potentially access, modify, or delete sensitive information while remaining undetected within the system.
Organizations affected by CVE-2017-2773 should implement immediate mitigation strategies to address the JWT validation weakness. The primary remediation involves upgrading to the patched versions of PCF Elastic Runtime that contain proper JWT algorithm validation logic, specifically versions 1.6.60, 1.7.41, 1.8.23, and 1.9.1 respectively. Security teams should also consider implementing additional monitoring and logging controls to detect suspicious authentication patterns that might indicate exploitation attempts. The vulnerability's classification aligns with ATT&CK technique T1566 which covers social engineering attacks, as the exploitation relies on manipulating authentication mechanisms rather than traditional credential theft methods. Additionally, organizations should review their JWT implementation practices and ensure that all token validation processes enforce strict algorithm constraints, particularly rejecting tokens that use the 'none' algorithm or other insecure signing methods. This vulnerability serves as a reminder of the critical importance of proper cryptographic validation in authentication systems and demonstrates how seemingly minor implementation flaws can create significant security risks in enterprise platforms.