CVE-2015-7794 in CG-WLNCM4G
Summary
by MITRE
Corega CG-WLNCM4G devices provide an open DNS resolver, which allows remote attackers to cause a denial of service (traffic amplification) via crafted queries.
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Analysis
by VulDB Data Team • 05/26/2018
The CVE-2015-7794 vulnerability affects Corega CG-WLNCM4G wireless router devices that expose an open DNS resolver configuration. This flaw represents a critical security issue within the realm of DNS amplification attacks and reflects the broader category of misconfigured network services that can be exploited for distributed denial of service (DDoS) operations. The vulnerability stems from the device's default configuration where the DNS resolver service is left accessible to external networks without proper access controls or rate limiting mechanisms. This configuration allows any remote attacker to leverage the device as an open relay for DNS queries, which can be manipulated to amplify network traffic volumes significantly. The affected devices typically operate with default settings that do not restrict DNS query forwarding to unauthorized external parties, creating an exploitable entry point for malicious actors seeking to launch large-scale traffic amplification attacks.
The technical exploitation of this vulnerability involves crafting specific DNS queries that can generate disproportionately large responses when forwarded through the open resolver. Attackers typically utilize DNS query types such as AXFR (zone transfer) or queries with large record sets that can cause the device to respond with significantly more data than the original request. The amplification factor can range from hundreds to thousands of times the original query size, making these attacks particularly effective for overwhelming target systems with traffic volume. This flaw directly relates to CWE-643, which addresses insufficient input validation in DNS resolution processes, and demonstrates how misconfigured network services can create dangerous attack vectors. The vulnerability exists at the application layer of the network stack where DNS services are improperly secured, allowing unauthorized access to network resources that should be protected from external traffic.
From an operational impact perspective, this vulnerability enables attackers to conduct massive DDoS attacks using the compromised devices as amplifiers in botnet operations. The affected Corega devices can be easily identified and exploited through automated scanning tools, making them attractive targets for malicious actors seeking to build large-scale attack infrastructures. The traffic amplification effect can quickly overwhelm network bandwidth and system resources at the target, causing legitimate service disruption. Security researchers have documented how these devices can be leveraged in DNS amplification attacks where a single query can generate hundreds of megabytes of response traffic, making them particularly dangerous for network administrators and service providers. The vulnerability also represents a significant concern for enterprise networks where such devices may be deployed without proper security hardening, creating potential attack vectors that can be exploited by threat actors without requiring advanced technical skills or significant resources.
Mitigation strategies for CVE-2015-7794 involve implementing proper network security controls and device configuration management practices. Network administrators should immediately disable unnecessary DNS resolver services on affected devices and implement access control lists to restrict DNS query forwarding to authorized internal networks only. The configuration should include rate limiting mechanisms to prevent abuse of the DNS service and enable logging of DNS queries for monitoring purposes. Security measures should also include regular firmware updates to address known vulnerabilities and ensure that devices are not running outdated software versions that may contain unpatched security flaws. Organizations should implement network segmentation to isolate IoT and networking devices from critical internal systems, reducing the potential impact of compromised devices. This vulnerability highlights the importance of adhering to the principle of least privilege and demonstrates how basic security misconfigurations can create significant operational risks. The remediation process should involve comprehensive network audits to identify all devices with similar vulnerabilities and ensure that proper security controls are implemented across the entire network infrastructure. Network security professionals should also consider implementing intrusion detection systems to monitor for suspicious DNS traffic patterns and establish incident response procedures for handling potential exploitation attempts.