CVE-2018-8929 in SSL VPN Client
Summary
by MITRE
Improper restriction of communication channel to intended endpoints vulnerability in HTTP daemon in Synology SSL VPN Client before 1.2.4-0224 allows remote attackers to conduct man-in-the-middle attacks via a crafted payload.
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Analysis
by VulDB Data Team • 04/03/2023
The vulnerability identified as CVE-2018-8929 represents a critical flaw in Synology SSL VPN Client's HTTP daemon implementation that fundamentally compromises the integrity of network communications. This weakness manifests as an improper restriction of communication channels to intended endpoints, creating a pathway for remote attackers to execute sophisticated man-in-the-middle attacks. The vulnerability specifically affects versions prior to 1.2.4-0224, indicating that Synology had not yet implemented adequate safeguards to prevent unauthorized interception of network traffic. The flaw exists within the SSL VPN client's handling of HTTP communications, where the system fails to properly validate or restrict the endpoints to which communication channels may be established, leaving network sessions vulnerable to malicious interference.
The technical nature of this vulnerability stems from inadequate validation mechanisms within the HTTP daemon that processes network requests. When users establish connections through the Synology SSL VPN Client, the system should enforce strict endpoint validation to ensure that communication occurs only with authorized servers and services. However, the vulnerability allows attackers to craft malicious payloads that can redirect or intercept communication flows, effectively bypassing the intended security boundaries. This improper restriction creates an environment where network traffic can be manipulated or monitored by unauthorized parties without detection, as the system does not adequately verify the authenticity or legitimacy of communication endpoints. The flaw operates at the protocol level, affecting how the SSL VPN client manages its network connections and validates remote endpoints.
The operational impact of this vulnerability extends beyond simple data interception, as it enables sophisticated attack vectors that can compromise entire network infrastructures. Remote attackers leveraging this vulnerability can perform man-in-the-middle attacks that allow them to eavesdrop on sensitive communications, modify data in transit, or even inject malicious content into network sessions. The implications are particularly severe for organizations relying on Synology SSL VPN solutions for secure remote access, as this vulnerability undermines the fundamental security assumptions of encrypted network communications. Network administrators may experience unauthorized access to confidential data, potential credential theft, and complete loss of trust in the VPN infrastructure. The vulnerability also creates opportunities for attackers to establish persistent access points within networks, as compromised communication channels can be used to maintain footholds for extended periods.
Organizations affected by CVE-2018-8929 should prioritize immediate remediation through the installation of Synology SSL VPN Client version 1.2.4-0224 or later, which addresses the improper endpoint restriction issue. Security teams must also implement comprehensive network monitoring to detect potential exploitation attempts and establish network segmentation strategies to limit the potential damage from successful attacks. The vulnerability aligns with CWE-284, which addresses improper access control in communication channels, and maps to ATT&CK technique T1041, which covers data compression and encryption. Additional mitigations include implementing network intrusion detection systems, conducting regular security assessments of VPN configurations, and establishing robust certificate management practices. Organizations should also consider deploying additional security layers such as network access control and endpoint detection and response solutions to provide defense-in-depth against similar vulnerabilities. The incident underscores the critical importance of maintaining up-to-date security software and implementing comprehensive security governance practices to prevent exploitation of communication channel vulnerabilities.