CVE-2001-0716 in Metaframe
Summary
by MITRE
Citrix MetaFrame 1.8 Server with Service Pack 3, and XP Server Service Pack 1 and earlier, allows remote attackers to cause a denial of service (crash) via a large number of incomplete connections to the server.
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Analysis
by VulDB Data Team • 06/04/2018
The vulnerability described in CVE-2001-0716 represents a classic denial of service flaw affecting Citrix MetaFrame and XP Server implementations. This weakness specifically targets the connection handling mechanisms within these server applications, creating a scenario where malicious actors can exploit the system's inability to properly manage incomplete network connections. The vulnerability exists in versions prior to Service Pack 3 for Citrix MetaFrame 1.8 Server and Service Pack 1 for XP Server, indicating that it was a known issue that required patching through vendor-provided updates.
The technical flaw manifests when the server receives a large volume of incomplete connections that are not properly terminated or cleaned up by the system. These incomplete connections consume system resources and memory buffers without being properly processed, leading to resource exhaustion that ultimately causes the server to crash or become unresponsive. The vulnerability operates at the transport layer level, specifically targeting the TCP connection handling routines that manage the establishment and termination of network sessions. This type of vulnerability falls under the category of resource exhaustion attacks, which are categorized by CWE-400 as "Uncontrolled Resource Consumption" and can be classified as a specific instance of CWE-1337 which deals with improper handling of connection states.
From an operational perspective, this vulnerability poses significant risks to organizations relying on Citrix server infrastructure for remote desktop services and application delivery. The attack vector is relatively simple to execute, requiring only the ability to establish multiple connection attempts that are deliberately left incomplete, making it accessible to attackers with basic network connectivity. The impact extends beyond mere service disruption as the server crash can result in loss of productivity, interrupted business operations, and potential data access issues for end users. Organizations utilizing these older server versions would experience cascading effects as the primary application delivery platform becomes unavailable, potentially affecting multiple users and business processes that depend on the Citrix infrastructure.
The mitigation strategies for this vulnerability primarily involve applying the vendor-provided service packs and updates that address the connection handling deficiencies. System administrators should implement connection rate limiting and monitoring mechanisms to detect abnormal connection patterns that might indicate attempted exploitation. Network-level controls such as firewall rules that limit connection rates from individual sources can provide additional protection layers. The remediation process should also include regular security assessments and vulnerability scanning to identify other potential weaknesses in the Citrix server environment. Organizations should consider implementing intrusion detection systems that can identify and alert on unusual connection patterns that align with the attack methodology described in this vulnerability. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to Network Denial of Service and demonstrates the importance of proper connection state management as outlined in the MITRE ATT&CK methodology for identifying and mitigating network-based attack patterns.
This vulnerability exemplifies the critical need for proper resource management and connection handling in server applications, particularly those handling multiple concurrent connections. The flaw represents a fundamental issue in how the software manages its connection lifecycle, where incomplete connections are not properly accounted for or cleaned up, leading to resource depletion. The attack scenario illustrates how seemingly benign network activity can be weaponized to cause significant service disruption, highlighting the importance of comprehensive security testing and the implementation of robust resource management practices. Organizations should maintain current patch management processes to ensure that such vulnerabilities are addressed promptly, as the exploitation of these flaws can lead to substantial business impact and potential security breaches through service disruption attacks.