CVE-2018-13296 in MailPlus Server
Summary
by MITRE
Uncontrolled resource consumption vulnerability in TLS configuration in Synology MailPlus Server before 2.0.5-0606 allows remote attackers to conduct denial-of-service attacks via client-initiated renegotiation.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 08/21/2023
The vulnerability identified as CVE-2018-13296 represents a critical uncontrolled resource consumption flaw within the TLS configuration of Synology MailPlus Server versions prior to 2.0.5-0606. This weakness specifically targets the server's handling of client-initiated TLS renegotiation processes, creating a pathway for remote attackers to execute denial-of-service attacks against affected systems. The vulnerability stems from insufficient resource management during the TLS renegotiation phase, where the server fails to properly limit or monitor the consumption of computational resources during these operations.
The technical implementation of this vulnerability exploits the inherent characteristics of TLS renegotiation protocols, particularly the way the MailPlus Server processes renegotiation requests from remote clients. When a client initiates a TLS renegotiation, the server must validate credentials and potentially reauthenticate the connection, which consumes significant computational resources including memory allocation, CPU cycles, and connection handling capacity. The flaw occurs because the server does not implement adequate rate limiting or resource consumption thresholds for renegotiation requests, allowing malicious actors to continuously initiate renegotiation sequences that gradually exhaust available system resources.
From an operational perspective, this vulnerability poses significant risks to organizations relying on Synology MailPlus Server for email services, as it can effectively render the mail server unavailable to legitimate users. Attackers can consume system resources through repeated renegotiation attempts, leading to memory exhaustion, CPU overload, and ultimately service disruption. The impact extends beyond simple availability issues as the resource consumption can affect other services running on the same server infrastructure, potentially causing cascading failures throughout the organization's email ecosystem. The vulnerability is particularly concerning because TLS renegotiation is a legitimate protocol feature that should be supported, yet the implementation fails to distinguish between normal usage patterns and malicious resource exhaustion attempts.
The vulnerability aligns with CWE-400, which addresses uncontrolled resource consumption, and specifically relates to improper handling of TLS protocol features in server implementations. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for network denial of service, where adversaries leverage protocol-specific weaknesses to exhaust system resources. The attack vector requires minimal privileges as it operates entirely at the network layer, making it accessible to remote attackers without requiring authentication. The lack of proper resource limits in the TLS configuration creates a persistent vulnerability that can be exploited repeatedly until the system is patched or restarted.
Organizations should immediately implement mitigation strategies including disabling TLS renegotiation where possible, implementing rate limiting for renegotiation requests, and applying the available security patches to upgrade to Synology MailPlus Server version 2.0.5-0606 or later. Network monitoring should be enhanced to detect unusual patterns of renegotiation activity, and system administrators should configure appropriate resource limits and connection timeouts to prevent resource exhaustion. Additionally, implementing intrusion detection systems that can identify and block excessive renegotiation attempts provides an additional layer of protection against this specific attack vector. The vulnerability underscores the critical importance of proper TLS protocol implementation and resource management in server applications, particularly in email services that handle high volumes of concurrent connections and authentication requests.