CVE-2018-20809 in Pulse Connect Secure
Summary
by MITRE
A crafted message can cause the web server to crash with Pulse Secure Pulse Connect Secure (PCS) 8.3RX before 8.3R5 and Pulse Policy Secure 5.4RX before 5.4R5. This is not applicable to PCS 8.1RX.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 06/28/2020
This vulnerability affects Pulse Secure Pulse Connect Secure and Pulse Policy Secure appliances running specific versions of the software, creating a remote denial of service condition that can be exploited by attackers who craft malicious messages. The flaw exists in the web server component of these security appliances, which are widely deployed in enterprise environments for remote access and network security management. The vulnerability specifically impacts versions 8.3RX before 8.3R5 and 5.4RX before 5.4R5, while versions 8.1RX are not affected, indicating a regression or specific code change that introduced this weakness. This type of vulnerability falls under CWE-129 Input Validation, as it represents a failure to properly validate incoming data before processing, and can be categorized under ATT&CK technique T1499.002 for network denial of service attacks.
The technical exploitation of this vulnerability occurs when an attacker sends a specially crafted message to the affected web server, which then processes this malformed input without proper validation mechanisms. The web server crashes or becomes unresponsive as a result of this processing failure, effectively rendering the security appliance unusable for its intended purpose. The crash typically occurs during message parsing or handling routines where the server fails to properly handle unexpected input formats, leading to memory corruption or stack overflow conditions that cause the service to terminate. This behavior aligns with CWE-121 Stack-based Buffer Overflow or similar memory corruption vulnerabilities that can be triggered by malformed input data.
The operational impact of this vulnerability extends beyond simple service disruption, as these appliances are critical infrastructure components in many enterprise security architectures. When compromised, the affected appliances can no longer provide remote access services, VPN functionality, or policy enforcement capabilities that organizations rely upon for secure network access. This creates significant business disruption and potentially leaves networks vulnerable to unauthorized access while the appliance is offline. The vulnerability affects organizations that depend on Pulse Secure appliances for remote workforce access, branch office connectivity, and secure network policy enforcement, making it particularly concerning for companies with distributed workforces or remote access requirements.
Organizations should immediately implement mitigations including applying the vendor-provided security patches that address this vulnerability in versions 8.3R5 and 5.4R5, respectively. Network segmentation and access controls should be implemented to limit exposure of these appliances to untrusted networks, while monitoring systems should be configured to detect unusual traffic patterns or service disruptions. Additionally, organizations should consider implementing intrusion detection systems that can identify attempts to send malformed messages to these appliances, and maintain detailed incident response procedures for dealing with service disruptions. The vulnerability demonstrates the importance of keeping security infrastructure components updated and highlights the need for proper input validation and error handling in web server implementations, aligning with industry best practices for secure coding and vulnerability management.