CVE-2020-29238 in ExpressVPN
Summary
by MITRE • 03/10/2021
An integer buffer overflow in the Nginx webserver of ExpressVPN Router version 1 allows remote attackers to obtain sensitive information when the server running as reverse proxy via specially crafted request.
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Analysis
by VulDB Data Team • 11/23/2024
The vulnerability identified as CVE-2020-29238 represents a critical integer buffer overflow flaw within the Nginx webserver component of ExpressVPN Router version 1. This vulnerability manifests when the server operates in reverse proxy mode, creating a pathway for remote attackers to exploit the system and extract sensitive information from the affected environment. The flaw stems from improper input validation and memory handling within the Nginx implementation, specifically when processing specially crafted HTTP requests that manipulate integer values beyond their allocated buffer boundaries.
The technical execution of this vulnerability involves attackers sending malformed requests that trigger integer overflow conditions within the Nginx reverse proxy functionality. When the server processes these malicious inputs, the integer values exceed their defined limits causing buffer overflow conditions that can lead to information disclosure. The vulnerability is categorized under CWE-121 as an improper restriction of operations within the buffer boundary, which directly enables attackers to read beyond allocated memory regions and potentially access sensitive data such as memory contents, configuration details, or other confidential information stored in adjacent memory locations.
From an operational perspective, this vulnerability poses significant risks to organizations relying on ExpressVPN Router version 1 for their network infrastructure. The remote exploit capability means attackers can target the system from external networks without requiring physical access or local credentials, making the attack surface particularly concerning for enterprise environments. The information disclosure aspect can potentially expose network configurations, user data, or other sensitive operational details that could facilitate further attacks or compromise the overall security posture of the affected network infrastructure.
The impact of this vulnerability extends beyond simple information disclosure, as it can serve as a stepping stone for more sophisticated attacks within the compromised network. Attackers may leverage the disclosed information to conduct targeted attacks against other systems or to establish persistence within the network. This aligns with ATT&CK technique T1005 where adversaries collect data from network devices, potentially using the information to identify network topology, service configurations, or other sensitive details that could be exploited in subsequent phases of an attack campaign.
Mitigation strategies for CVE-2020-29238 should prioritize immediate patching of the ExpressVPN Router firmware to address the integer buffer overflow condition. Organizations should also implement network monitoring to detect unusual traffic patterns that may indicate exploitation attempts, particularly focusing on malformed HTTP requests targeting the reverse proxy functionality. Additional defensive measures include implementing strict input validation for all incoming requests, configuring proper access controls to limit exposure, and conducting regular security assessments of network infrastructure components to identify similar vulnerabilities that may exist in other systems or applications. Network segmentation and intrusion detection systems should be deployed to minimize potential damage from successful exploitation attempts and to provide early warning of compromise indicators.