CVE-2011-2882 in Access Gateway
Summary
by MITRE
Stack-based buffer overflow in 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 allows remote attackers to execute arbitrary code via crafted HTTP header data.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 05/25/2025
The vulnerability CVE-2011-2882 represents a critical stack-based buffer overflow affecting Citrix Access Gateway Enterprise Edition versions prior to specific patch releases. This flaw exists within the NSEPA.NsepaCtrl.1 ActiveX control component, specifically in the nsepa.ocx library file that forms part of Citrix's secure access infrastructure. The vulnerability manifests when the affected ActiveX control processes HTTP header data, creating a condition where maliciously crafted input can exceed the allocated buffer space on the stack. Such buffer overflows are particularly dangerous because they can be exploited to overwrite adjacent memory locations, potentially allowing attackers to execute arbitrary code with the privileges of the affected application.
The technical exploitation of this vulnerability occurs through remote code execution via crafted HTTP header data, making it particularly concerning for network-based attacks. When a vulnerable Citrix Access Gateway system processes HTTP requests containing specially crafted headers, the NSEPA.NsepaCtrl.1 ActiveX control fails to properly validate input length, leading to a stack buffer overflow condition. This type of vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is classified as a fundamental memory safety issue in software development. The attack vector is particularly dangerous because it can be initiated through standard web browser interactions, requiring no special privileges or local access from the attacker's perspective.
The operational impact of CVE-2011-2882 extends beyond simple code execution, as it can enable complete system compromise of affected Citrix Access Gateway appliances. Organizations relying on these security appliances for remote access and VPN services face significant risk when exposed to this vulnerability, as successful exploitation could lead to unauthorized access to corporate networks, data exfiltration, and potential lateral movement within the attacked environment. The vulnerability affects multiple Citrix versions including 8.1, 9.0, and 9.1, indicating a widespread exposure across the product line. This type of remote code execution vulnerability is categorized under ATT&CK technique T1203 Exploitation for Client Execution, which represents a common attack pattern where adversaries leverage application vulnerabilities to gain code execution on target systems.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected Citrix Access Gateway systems to versions 8.1-67.7, 9.0-70.5, and 9.1-96.4 or later. Organizations should also implement network-based controls such as web application firewalls to filter suspicious HTTP headers and monitor for exploitation attempts. Additional defensive measures include disabling ActiveX controls in browser configurations where possible, implementing network segmentation to limit access to vulnerable appliances, and conducting thorough vulnerability assessments to identify other potentially affected systems. The vulnerability highlights the importance of proper input validation and memory safety practices in software development, particularly for components that process untrusted network data. Security teams should also consider implementing intrusion detection systems to monitor for exploitation attempts and maintain comprehensive incident response procedures for handling potential compromise scenarios.