CVE-2021-22927 in ADC
Summary
by MITRE • 08/06/2021
A session fixation vulnerability exists in Citrix ADC and Citrix Gateway 13.0-82.45 when configured SAML service provider that could allow an attacker to hijack a session.
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Analysis
by VulDB Data Team • 08/10/2021
The vulnerability identified as CVE-2021-22927 represents a critical session fixation flaw within Citrix ADC and Citrix Gateway appliances running version 13.0-82.45 with SAML service provider configurations. This weakness arises from the improper handling of session identifiers during authentication processes, creating a pathway for malicious actors to exploit the system's session management mechanisms. The vulnerability specifically impacts environments where Citrix appliances are configured to function as SAML service providers, which is a common deployment pattern in enterprise single sign-on implementations. Organizations utilizing Citrix solutions for identity federation and access control are particularly at risk when these appliances are configured with SAML authentication protocols, as the flaw allows attackers to maintain persistent access to user sessions through the exploitation of session fixation techniques.
The technical implementation of this vulnerability stems from the failure of the Citrix appliance to properly invalidate or regenerate session identifiers when transitioning from an anonymous to an authenticated state. When users authenticate through SAML service provider configurations, the system should generate new session tokens to prevent session hijacking attempts. However, the flaw allows attackers to obtain valid session tokens before authentication and then use those same tokens after successful authentication, effectively enabling session fixation attacks. This behavior violates fundamental security principles of session management and represents a direct violation of the session management controls defined in industry standards such as CWE-384, which specifically addresses session fixation vulnerabilities. The vulnerability's impact is amplified by the fact that Citrix ADC and Gateway appliances often serve as critical infrastructure components in enterprise environments, making successful exploitation potentially devastating for organizational security postures.
The operational impact of CVE-2021-22927 extends beyond simple session hijacking, as it enables attackers to gain unauthorized access to protected resources and potentially escalate privileges within the affected environments. Attackers can leverage this vulnerability to maintain persistent access to user sessions, monitor network traffic, and potentially move laterally within the network infrastructure. The attack vector typically involves an attacker obtaining a valid session token, either through prior access or by exploiting other vulnerabilities, and then using this token to hijack legitimate user sessions after authentication. This vulnerability aligns with ATT&CK technique T1563.002, which describes "Access Token Manipulation" and can be exploited to gain unauthorized access to systems and data. Organizations may experience significant security breaches, data exfiltration, and unauthorized access to sensitive enterprise resources, particularly when these appliances are deployed in environments with high-value assets or critical business processes.
Mitigation strategies for CVE-2021-22927 require immediate implementation of vendor-provided patches and updates to address the session fixation vulnerability in Citrix ADC and Gateway appliances. Organizations should prioritize upgrading their Citrix appliances to versions that contain the necessary security fixes, as these updates typically include proper session token regeneration mechanisms and enhanced session management controls. Network administrators should also implement additional monitoring and detection measures to identify potential exploitation attempts, including logging and analyzing session creation and authentication events. Configuration hardening practices should be applied to ensure that SAML service provider configurations follow security best practices, including proper session token handling and regular token rotation. Organizations should consider implementing additional security controls such as multi-factor authentication, network segmentation, and enhanced access controls to reduce the potential impact of successful exploitation attempts. The remediation process should also include comprehensive vulnerability assessments to identify any other potentially affected systems within the enterprise infrastructure, as similar session management flaws may exist in other components of the organization's security infrastructure.