CVE-2011-2883 in Access Gateway
Summary
by MITRE
The NSEPA.NsepaCtrl.1 ActiveX control in nsepa.ocx in Citrix Access Gateway Enterprise Edition 8.1 before 8.1-67.7, 9.0 before 9.0-70.5, and 9.1 before 9.1-96.4 attempts to validate signed DLLs by checking the certificate subject, not the signature, which allows man-in-the-middle attackers to execute arbitrary code via HTTP header data referencing a DLL that was signed with a crafted certificate.
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Analysis
by VulDB Data Team • 11/15/2021
The vulnerability identified as CVE-2011-2883 resides within the NSEPA.NsepaCtrl.1 ActiveX control component of Citrix Access Gateway Enterprise Edition versions 8.1 prior to 8.1-67.7, 9.0 prior to 9.0-70.5, and 9.1 prior to 9.1-96.4. This flaw represents a critical security weakness in the certificate validation mechanism that governs signed DLL loading processes within the affected Citrix products. The vulnerability stems from a fundamental design flaw in how the system validates digital signatures, specifically by relying on certificate subject verification rather than proper signature validation. This misconfiguration creates an exploitable condition that allows malicious actors to bypass security controls through carefully crafted HTTP header data.
The technical implementation of this vulnerability demonstrates a clear violation of proper cryptographic validation practices as outlined in industry standards. The ActiveX control performs certificate subject validation instead of signature verification, which creates a fundamental security gap that can be exploited by attackers. This approach fails to properly authenticate the source and integrity of loaded DLLs, as the system accepts signed DLLs even when the certificate subject has been manipulated or forged. The vulnerability operates at the core of software security mechanisms, where the certificate subject field can be manipulated without breaking the signature validation, allowing attackers to execute arbitrary code through HTTP header data that references DLLs signed with crafted certificates. This issue directly relates to CWE-311, which addresses the absence of proper cryptographic protection for sensitive data, and CWE-310, concerning cryptographic issues that affect data integrity.
The operational impact of this vulnerability is severe and far-reaching within enterprise environments that utilize Citrix Access Gateway solutions. Attackers can leverage this weakness to perform man-in-the-middle attacks, executing arbitrary code on vulnerable systems without requiring elevated privileges or authentication. The attack vector through HTTP header data means that exploitation can occur during normal network communication, making detection difficult and potentially allowing persistent access to corporate networks. This vulnerability enables attackers to compromise the integrity of the affected systems, potentially leading to full system compromise, data exfiltration, and lateral movement within network environments. The exploitation process allows for privilege escalation and persistent access, making it particularly dangerous for organizations relying on Citrix Access Gateway for secure remote access solutions.
Mitigation strategies for CVE-2011-2883 should prioritize immediate patch deployment from Citrix, ensuring all affected versions are updated to the patched releases mentioned in the advisory. Organizations must also implement network segmentation and monitoring to detect suspicious HTTP header data patterns that could indicate exploitation attempts. Security controls should include disabling unnecessary ActiveX controls and implementing proper certificate validation policies that enforce signature verification rather than subject validation. Additionally, organizations should conduct comprehensive vulnerability assessments to identify all instances of the vulnerable ActiveX control within their environments and implement network-based intrusion detection systems to monitor for exploitation attempts. The remediation process should align with ATT&CK technique T1190, which addresses exploitation of remote services, and T1059, covering command and script interpretation, as these techniques are commonly employed in exploiting such vulnerabilities. Regular security updates and patch management processes must be strengthened to prevent similar issues in other software components that may rely on similar certificate validation mechanisms.