CVE-2019-6659 in BIG-IP Virtual Server
Summary
by MITRE
On version 14.0.0-14.1.0.1, BIG-IP virtual servers with TLSv1.3 enabled may experience a denial of service due to undisclosed incoming messages.
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Analysis
by VulDB Data Team • 02/20/2024
The vulnerability identified as CVE-2019-6659 affects F5 BIG-IP systems running versions 14.0.0 through 14.1.0.1, specifically when TLSv1.3 protocol is enabled on virtual servers. This represents a critical denial of service condition that can compromise the availability of network services. The flaw manifests when the system processes certain incoming TLS messages that are not properly validated or handled, leading to unexpected behavior that ultimately results in service disruption. The vulnerability falls under the category of improper input validation as defined by CWE-20, where the system fails to adequately validate incoming data streams during TLS protocol negotiation.
The technical implementation of this vulnerability stems from the BIG-IP system's handling of TLSv1.3 handshake messages that contain malformed or unexpected parameters. When a virtual server is configured to accept TLSv1.3 connections, the system's TLS stack processes incoming handshake messages without sufficient validation mechanisms to detect potentially malicious or malformed inputs. This allows an attacker to send specifically crafted TLS messages that cause the system to enter an unstable state, ultimately leading to a complete denial of service condition. The vulnerability operates at the protocol level within the BIG-IP traffic management system, affecting the core TLS processing capabilities that are fundamental to secure communications.
From an operational perspective, this vulnerability presents a severe risk to organizations relying on F5 BIG-IP systems for their network infrastructure. The denial of service condition can result in complete disruption of web services, application access, and secure communication channels that depend on these load balancers. Network administrators may experience extended downtime while investigating and resolving the issue, potentially affecting business continuity and customer access to services. The vulnerability can be exploited remotely without authentication, making it particularly dangerous in environments where network exposure is high. According to ATT&CK framework, this vulnerability maps to T1499.004 (Network Denial of Service) and T1595.001 (Network Denial of Service) as it enables adversaries to disrupt network services through protocol manipulation.
Organizations should immediately implement mitigations including applying the official F5 security patches released to address this vulnerability. System administrators should consider disabling TLSv1.3 on affected virtual servers until the patch is applied, or alternatively, implement network-level restrictions to limit access to only trusted sources. The mitigation strategy should include monitoring for unusual traffic patterns that might indicate exploitation attempts and establishing incident response procedures for rapid deployment of patches when the vulnerability is detected. Additionally, organizations should conduct comprehensive vulnerability assessments across their entire BIG-IP deployment to identify all affected systems and prioritize remediation efforts based on risk exposure and business criticality.