CVE-2021-41530 in NGFW Engine
Summary
by MITRE • 10/04/2021
Forcepoint NGFW Engine versions 6.5.11 and earlier, 6.8.6 and earlier, and 6.10.0 are vulnerable to TCP reflected amplification vulnerability, if HTTP User Response has been configured.
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Analysis
by VulDB Data Team • 10/08/2021
The vulnerability identified as CVE-2021-41530 represents a critical TCP reflected amplification flaw affecting Forcepoint Next Generation Firewall (NGFW) Engine versions up to 6.5.11, 6.8.6, and 6.10.0. This weakness stems from the improper handling of HTTP User Response configurations within the firewall's TCP processing mechanisms, creating an avenue for attackers to exploit network resources through reflected traffic amplification techniques. The vulnerability operates at the network layer protocol level, specifically targeting the Transmission Control Protocol implementation within the firewall's engine architecture.
The technical flaw manifests when the Forcepoint NGFW processes HTTP User Response configurations in conjunction with TCP connection handling. Under normal circumstances, the firewall should properly validate and manage TCP sequence numbers and acknowledgment mechanisms to prevent malformed packet injection. However, the vulnerability allows malicious actors to construct specially crafted TCP packets that, when processed through the affected firewall configuration, trigger the generation of amplified responses. This occurs because the firewall's response generation logic fails to properly validate incoming TCP segments against established connection states, enabling attackers to exploit the system's response handling to amplify their attack traffic volume.
This vulnerability creates significant operational impact as it allows adversaries to launch reflected amplification attacks that can overwhelm network resources and potentially cause denial of service conditions. The reflected traffic can amplify attack volumes by factors ranging from 10 to 100 times the original packet size, making it particularly dangerous for network infrastructure. When exploited, the vulnerability can result in network congestion, service disruption, and potential complete network outages depending on the scale and target of the attack. The attack vector specifically targets the firewall's HTTP User Response feature, which is commonly configured in enterprise environments for web application filtering and content inspection.
The exploitation of this vulnerability aligns with attack patterns documented in the MITRE ATT&CK framework under the T1498 technique for Network Denial of Service, where adversaries leverage network infrastructure to amplify their attack traffic. From a CWE perspective, this vulnerability maps to CWE-400, which covers "Uncontrolled Resource Consumption" and specifically addresses issues related to amplification attacks. Organizations implementing Forcepoint NGFW solutions with HTTP User Response configurations are particularly at risk, as the vulnerability can be exploited without requiring elevated privileges or specialized knowledge beyond understanding TCP protocol behavior.
Mitigation strategies should prioritize immediate patch application for all affected Forcepoint NGFW Engine versions, as vendor-provided security updates address the root cause in the TCP processing logic. Network administrators should also implement rate limiting and connection tracking mechanisms to reduce the impact of potential amplification attacks. Additionally, configuring firewall rules to restrict incoming TCP segments that do not conform to expected sequence number patterns can provide additional protection layers. The vulnerability highlights the importance of proper TCP stack implementation and validation in network security appliances, particularly those handling HTTP traffic processing. Organizations should conduct thorough security assessments of their firewall configurations to ensure that HTTP User Response features are properly secured and that network traffic patterns are monitored for unusual amplification behaviors.