CVE-2015-2809 in DiskStation Manager
Summary
by MITRE
The Multicast DNS (mDNS) responder in Synology DiskStation Manager (DSM) before 3.1 inadvertently responds to unicast queries with source addresses that are not link-local, which allows remote attackers to cause a denial of service (traffic amplification) or obtain potentially sensitive information via port-5353 UDP packets to the Avahi component.
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Analysis
by VulDB Data Team • 01/15/2025
The vulnerability identified as CVE-2015-2809 affects Synology DiskStation Manager (DSM) versions prior to 3.1, specifically within the Multicast DNS (mDNS) responder implementation. This flaw exists in the Avahi component which handles DNS resolution services for networked devices. The issue stems from improper handling of unicast DNS queries that originate from non-link-local source addresses, creating a security gap that can be exploited by remote attackers to manipulate network traffic patterns.
The technical flaw manifests when the mDNS responder processes incoming UDP packets on port 5353, which is the standard port for DNS resolution services. Normally, mDNS queries should only be accepted from link-local addresses to prevent unauthorized network participation. However, the Synology DSM implementation fails to properly validate source addresses, allowing queries from external IP addresses to trigger responses. This behavior creates a fundamental breakdown in the security model that governs mDNS operations and violates standard network security practices.
The operational impact of this vulnerability is significant and manifests through two primary attack vectors. First, the flaw enables traffic amplification attacks where remote attackers can send small queries to the DSM system and receive disproportionately large responses, potentially overwhelming network bandwidth and causing denial of service conditions. Second, the vulnerability allows for information disclosure risks as the system may inadvertently reveal internal network information through its responses to these malformed queries. This dual nature makes the vulnerability particularly dangerous as it can be used both for disruptive attacks and for reconnaissance purposes.
From a cybersecurity perspective, this vulnerability maps directly to CWE-200 (Information Exposure) and CWE-400 (Uncontrolled Resource Consumption) categories, representing information disclosure and denial of service risks respectively. The attack surface aligns with ATT&CK techniques such as T1498 (Network Denial of Service) and T1082 (System Information Discovery), as attackers can leverage this flaw to both disrupt services and gather network intelligence. The vulnerability also demonstrates poor input validation practices that violate fundamental security principles for network services.
Organizations should implement immediate mitigations including updating to Synology DSM version 3.1 or later, which contains the necessary patches to properly validate source addresses in mDNS queries. Network administrators should also consider implementing firewall rules that restrict access to port 5353 from external networks, effectively blocking unauthorized queries before they reach the vulnerable system. Additionally, monitoring for unusual traffic patterns on port 5353 can help detect exploitation attempts and provide early warning of potential attacks targeting this specific vulnerability.