CVE-2011-2593 in Access Gateway Plug-in
Summary
by MITRE
Integer 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 crafted Content-Length HTTP header, which triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 03/26/2022
The vulnerability identified as CVE-2011-2593 represents a critical integer overflow flaw within the Citrix Access Gateway Enterprise Edition Plug-in for Windows, specifically affecting versions prior to 9.3-57.5 and 10.0-69.4. This issue manifests in the StartEpa method of the nsepacom ActiveX control, which is implemented through the nsepa.exe executable component. The vulnerability operates at the intersection of software security and network protocol handling, creating a pathway for remote code execution through carefully crafted HTTP headers that exploit fundamental computational errors in the application's memory management.
The technical exploitation mechanism involves an integer overflow condition that occurs when processing HTTP Content-Length headers, where the overflow triggers a heap-based buffer overflow within the ActiveX control's memory space. This flaw stems from inadequate input validation and bounds checking within the StartEpa method, allowing attackers to manipulate the integer arithmetic to exceed the allocated buffer boundaries. The vulnerability is classified as a CWE-190 integer overflow, which represents a well-documented weakness in software development where arithmetic operations produce values that exceed the maximum representable value for the data type, leading to unpredictable behavior including buffer overflows and memory corruption.
From an operational perspective, this vulnerability presents a severe threat to organizations relying on Citrix Access Gateway Enterprise Edition for secure remote access solutions. Attackers can remotely execute arbitrary code on affected systems by simply crafting malicious HTTP requests with oversized Content-Length headers, potentially leading to complete system compromise. The attack vector is particularly dangerous because it requires no authentication and can be delivered through standard web traffic, making it ideal for automated exploitation campaigns. The heap-based buffer overflow creates opportunities for memory corruption that can be leveraged to overwrite critical program execution structures, enabling privilege escalation and persistent access to target networks.
The security implications extend beyond immediate code execution to encompass broader network compromise potential, as the vulnerability affects enterprise-level remote access solutions that often serve as gateways to internal corporate networks. Organizations utilizing affected Citrix versions face significant risk of unauthorized access to sensitive data and network resources, particularly in environments where the plug-in is used for remote desktop access and secure application delivery. The vulnerability's impact is amplified by the widespread deployment of Citrix Access Gateway solutions in enterprise environments, making it a prime target for sophisticated attack campaigns. Mitigation strategies must include immediate patching of affected systems to the recommended versions, along with network-level controls such as web application firewalls and HTTP header validation to prevent exploitation attempts.
The ATT&CK framework categorizes this vulnerability under the T1059 command and control execution technique, where attackers can leverage the remote code execution capability to establish persistent access. Additionally, the vulnerability aligns with T1210 exploitation of remote services, as it targets a service component accessible through standard network protocols. Organizations should implement comprehensive vulnerability management processes to address similar integer overflow issues in their software inventory, as these types of flaws often indicate broader architectural weaknesses in input validation and memory safety practices. The remediation approach should include not only patch deployment but also security awareness training for administrators and regular security assessments to identify potential integer overflow conditions in custom applications and third-party software components.