CVE-2017-9521 in DPC3939
Summary
by MITRE
The Comcast firmware on Cisco DPC3939 (firmware version dpc3939-P20-18-v303r20421733-160420a-CMCST); Cisco DPC3939 (firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST); Cisco DPC3939B (firmware version dpc3939b-v303r204217-150321a-CMCST); Cisco DPC3941T (firmware version DPC3941_2.5s3_PROD_sey); and Arris TG1682G (eMTA&DOCSIS version 10.0.132.SIP.PC20.CT, software version TG1682_2.2p7s2_PROD_sey) devices allows remote attackers to execute arbitrary code via a specific (but unstated) exposed service. NOTE: the scope of this CVE does NOT include the concept of "Unnecessary Services" in general; the scope is only a single service that is unnecessarily exposed, leading to remote code execution. The details of that service might be disclosed at a later date.
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Analysis
by VulDB Data Team • 12/29/2019
The vulnerability identified as CVE-2017-9521 affects multiple cable modem devices including Cisco DPC3939, DPC3939B, DPC3941T, and Arris TG1682G models. This represents a critical remote code execution flaw that stems from an unnecessarily exposed service within the device firmware. The affected devices operate with specific firmware versions that contain a service interface which should not be publicly accessible but remains exposed to remote network connections. The vulnerability specifically targets the firmware implementations of these devices, with the affected versions showing particular susceptibility to unauthorized remote exploitation. This flaw demonstrates poor network security configuration practices where essential services are exposed without proper authentication or access controls, creating a significant attack surface for malicious actors.
The technical nature of this vulnerability involves an exposed service that allows remote attackers to execute arbitrary code on the affected devices. This service operates outside of normal operational parameters and lacks appropriate security measures such as authentication mechanisms, input validation, or network segmentation. The service likely operates on a standard network port or protocol that enables remote communication without proper authorization checks. The unspecified nature of the service details suggests that the vulnerability stems from a specific implementation flaw where the service remains accessible to external networks rather than being properly isolated within the device's internal network architecture. This exposure creates a direct pathway for attackers to bypass normal security controls and gain unauthorized access to the device's operating system.
The operational impact of this vulnerability is severe and far-reaching for network administrators and device owners. Remote code execution capabilities allow attackers to completely compromise the affected devices, potentially leading to complete network infiltration, data exfiltration, or disruption of service. The vulnerability affects devices that typically operate in residential and small business environments, making them attractive targets for attackers seeking to establish persistent access points or launch further attacks. The scope limitation to a single exposed service indicates that while the vulnerability is specific, it provides attackers with full system control, potentially enabling them to modify device configurations, install malicious software, or use the compromised devices as launching points for attacks against other network segments.
Security professionals should immediately implement network segmentation to isolate affected devices from critical network infrastructure and external networks. The recommended mitigation strategies include disabling or removing the unnecessarily exposed service from the device configuration, implementing proper firewall rules to restrict access to only authorized personnel, and conducting thorough network scans to identify any other potentially exposed services. Organizations should also consider deploying intrusion detection systems to monitor for suspicious network activity originating from these devices. The vulnerability aligns with CWE-915 which addresses improper control of a resource through mechanism, and relates to ATT&CK technique T1059 for executing commands through remote access tools. Regular firmware updates and security audits should be implemented to prevent similar exposure of services in future deployments. Device manufacturers should ensure proper default configurations that minimize exposed attack surfaces and implement robust access control mechanisms to prevent unauthorized remote access to critical system functions.