CVE-2017-1000071 in phpCAS
Summary
by MITRE
Jasig phpCAS version 1.3.4 is vulnerable to an authentication bypass in the validateCAS20 function when configured to authenticate against an old CAS server.
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Analysis
by VulDB Data Team • 12/12/2022
The vulnerability identified as CVE-2017-1000071 affects Jasig phpCAS version 1.3.4 and represents a critical authentication bypass flaw within the validateCAS20 function. This issue specifically manifests when the phpCAS library is configured to authenticate against older CAS (Central Authentication Service) servers, creating a significant security weakness that could allow unauthorized access to protected systems. The vulnerability stems from improper validation of authentication responses from legacy CAS implementations, where the library fails to adequately verify the authenticity of the authentication tokens provided by the server.
The technical flaw resides in the validateCAS20 function's handling of CAS server responses, particularly when interfacing with older CAS server versions that may not strictly adhere to the current authentication protocol standards. This function is designed to validate CAS 2.0 protocol responses but contains a logic error that permits forged authentication responses to be accepted as valid. The vulnerability exploits weaknesses in the response validation mechanism where the library does not properly check the integrity of the service ticket or the assertion provided by the CAS server. This flaw is categorized under CWE-287 which addresses improper authentication, and aligns with ATT&CK technique T1078 for valid accounts, as it allows attackers to bypass authentication entirely.
The operational impact of this vulnerability is substantial as it enables attackers to gain unauthorized access to systems protected by phpCAS authentication. An attacker who can manipulate or intercept the communication between the phpCAS client and the CAS server could potentially forge valid authentication responses, thereby bypassing the entire authentication mechanism. This creates a pathway for privilege escalation and unauthorized system access, particularly in environments where phpCAS is used to secure web applications, portals, or services that rely on centralized authentication. The vulnerability affects organizations using legacy CAS infrastructure and demonstrates how outdated security protocols can create persistent risks in modern authentication systems.
Mitigation strategies for CVE-2017-1000071 include immediate upgrading of the phpCAS library to a patched version that properly validates CAS server responses and implements robust authentication verification mechanisms. Organizations should also consider implementing network-level monitoring to detect anomalous authentication patterns and ensure that CAS servers are updated to current standards. The fix typically involves strengthening the validateCAS20 function to properly verify the integrity of authentication tokens and implement additional validation checks that prevent forged responses from being accepted. Security teams should conduct comprehensive audits of all systems using phpCAS to identify potential exploitation vectors and ensure that all authentication components are properly configured according to current security best practices. Additionally, implementing multi-factor authentication and regular security assessments can provide additional defense layers against potential exploitation of this vulnerability.