CVE-2011-2592 in Access Gateway Plugin
Summary
by MITRE
Heap-based buffer overflow in the StartEpa method in the nsepacom ActiveX control (nsepa.exe) in Citrix Access Gateway Enterprise Edition Plug-in for Windows 9.x before 9.3-57.5 and 10.0 before 10.0-69.4 allows remote attackers to execute arbitrary code via a long CSEC HTTP response header.
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Analysis
by VulDB Data Team • 03/27/2021
The vulnerability identified as CVE-2011-2592 represents a critical heap-based buffer overflow flaw within the Citrix Access Gateway Enterprise Edition Plug-in for Windows. This vulnerability specifically affects the nsepacom ActiveX control, which is implemented through the nsepa.exe executable component. The issue manifests within the StartEpa method where insufficient input validation allows attackers to exploit memory corruption through malformed HTTP response headers. The affected versions include Citrix Access Gateway Enterprise Edition 9.x prior to 9.3-57.5 and 10.0 prior to 10.0-69.4, indicating a prolonged period of exposure where organizations were vulnerable to this type of attack vector.
The technical exploitation of this vulnerability occurs through a carefully crafted CSEC HTTP response header that exceeds the allocated buffer space within the StartEpa method. When the ActiveX control processes this oversized header, it fails to properly bounds-check the input data before copying it into a fixed-size heap buffer. This fundamental flaw in memory management creates an opportunity for attackers to overwrite adjacent memory locations, potentially leading to arbitrary code execution. The heap-based nature of the overflow means that the attacker can manipulate memory layout to redirect program execution flow, making this vulnerability particularly dangerous for remote code execution scenarios. This type of vulnerability is classified under CWE-121 as heap-based buffer overflow, which falls under the broader category of memory safety issues in software development.
The operational impact of CVE-2011-2592 extends beyond simple privilege escalation as it provides attackers with complete system compromise capabilities when successfully exploited. Organizations relying on Citrix Access Gateway Enterprise Edition for secure remote access are at significant risk, as this vulnerability can be triggered through web-based attacks without requiring any authentication or local access. The attack surface is particularly concerning given that ActiveX controls are typically executed within web browser contexts, making exploitation possible through standard web browsing activities. This vulnerability aligns with ATT&CK technique T1059.007 for command and script interpreter execution, as successful exploitation could lead to full system compromise and persistent access. The remote execution capability makes this vulnerability particularly attractive to threat actors targeting enterprise networks, as it can be exploited from outside the organization's perimeter through web-based attack vectors.
Mitigation strategies for CVE-2011-2592 should prioritize immediate patching of affected Citrix Access Gateway Enterprise Edition versions to the recommended security updates. Organizations should implement network-level protections such as web application firewalls and HTTP header filtering to prevent malicious CSEC headers from reaching vulnerable systems. The ActiveX control should be disabled or removed from systems where it is not absolutely required, as the attack surface can be reduced through proper access control. Additionally, network segmentation and monitoring should be enhanced to detect unusual HTTP response patterns that might indicate exploitation attempts. Security teams should also consider implementing application whitelisting policies to prevent execution of untrusted ActiveX controls and maintain regular vulnerability assessments to identify similar memory corruption issues. The remediation process should include thorough testing of patched systems to ensure that the vulnerability is fully addressed without introducing new compatibility issues.