CVE-2020-8299 in ADC
Summary
by MITRE • 06/16/2021
Citrix ADC and Citrix/NetScaler Gateway 13.0 before 13.0-76.29, 12.1-61.18, 11.1-65.20, Citrix ADC 12.1-FIPS before 12.1-55.238, and Citrix SD-WAN WANOP Edition before 11.4.0, 11.3.2, 11.3.1a, 11.2.3a, 11.1.2c, 10.2.9a suffers from uncontrolled resource consumption by way of a network-based denial-of-service from within the same Layer 2 network segment. Note that the attacker must be in the same Layer 2 network segment as the vulnerable appliance.
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Analysis
by VulDB Data Team • 06/19/2021
Citrix ADC and Citrix NetScaler Gateway appliances are vulnerable to a denial-of-service condition that stems from uncontrolled resource consumption within network-based attacks. This vulnerability affects multiple versions of Citrix ADC and SD-WAN products, specifically targeting versions prior to 13.0-76.29, 12.1-61.18, 11.1-65.20, 12.1-FIPS before 12.1-55.238, and various SD-WAN WANOP Edition releases. The flaw manifests when an attacker operates within the same Layer 2 network segment as the vulnerable appliance, enabling them to consume system resources without proper bounds, ultimately leading to service disruption.
The technical mechanism behind this vulnerability involves the improper handling of network traffic within the appliance's resource management system. When malicious packets are sent from within the same Layer 2 network segment, the system fails to adequately limit resource allocation for processing these requests. This leads to a gradual exhaustion of available system resources such as memory, CPU cycles, and connection handling capabilities. The vulnerability is classified as a resource exhaustion attack where the attacker can manipulate the appliance's behavior to consume resources at an unsustainable rate. This behavior aligns with CWE-400 which describes improper resource management allowing attackers to cause resource exhaustion.
From an operational perspective, the impact of this vulnerability is significant as it allows attackers with local network access to disrupt critical infrastructure services. The requirement for the attacker to be within the same Layer 2 network segment limits the attack surface but does not eliminate the risk entirely, particularly in environments where network segmentation is not properly enforced. Organizations using these vulnerable appliances face potential service interruptions that could affect authentication services, load balancing, and application delivery functions. The vulnerability affects the core functionality of Citrix appliances that are widely deployed in enterprise environments for traffic management and security services.
The attack vector is particularly concerning because it requires minimal privileges to execute successfully. An attacker only needs access to the same network segment as the vulnerable appliance, which can be achieved through various means such as network compromise, physical access, or network misconfigurations. This makes the vulnerability exploitable in scenarios where network boundaries are not properly maintained or where attackers have gained access to internal network segments. The attack can be executed with relatively simple network tools and does not require advanced exploitation techniques, making it accessible to a broad range of threat actors.
Organizations should implement immediate mitigations including network segmentation to prevent unauthorized access to Layer 2 segments containing vulnerable appliances, applying the latest security patches provided by Citrix, and monitoring network traffic for unusual resource consumption patterns. The recommended remediation involves updating all affected Citrix ADC and SD-WAN appliances to versions that contain the appropriate fixes for this vulnerability. Additionally, implementing network access controls and firewall rules to limit unnecessary traffic to these appliances can help reduce the attack surface. This vulnerability also aligns with ATT&CK technique T1499 which covers network denial-of-service attacks and demonstrates the importance of proper resource management in network appliances.
The vulnerability represents a critical weakness in the resource management architecture of Citrix appliances and highlights the importance of implementing proper bounds checking and resource allocation controls. Organizations should conduct thorough assessments of their network infrastructure to identify all vulnerable appliances and ensure proper patch management procedures are in place. Regular monitoring of system resources and network traffic patterns can help detect potential exploitation attempts and provide early warning of ongoing attacks. This vulnerability underscores the necessity of maintaining up-to-date security measures and proper network segmentation practices to protect against both external and internal threats.