CVE-2017-9487 in DPC3939
Summary
by MITRE
The Comcast firmware on Cisco DPC3939 (firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST) and DPC3941T (firmware version DPC3941_2.5s3_PROD_sey) devices allows remote attackers to discover a WAN IPv6 IP address by leveraging knowledge of the CM MAC address.
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Analysis
by VulDB Data Team • 11/02/2019
The vulnerability identified as CVE-2017-9487 affects Cisco DPC3939 and DPC3941T cable modem devices running specific firmware versions, representing a significant security flaw in the broadband gateway infrastructure that serves millions of customers. This issue stems from insufficiently protected network configuration information disclosure mechanisms within the modem firmware, specifically exposing WAN IPv6 addressing details to unauthorized parties who possess knowledge of the Cable Modem's Media Access Control address. The vulnerability exists in the context of cable modem deployments where devices operate as critical entry points to home networks and corporate environments, making them attractive targets for attackers seeking to map network topology and identify potential attack vectors.
The technical flaw manifests through a design weakness in how the modem firmware handles IPv6 address discovery requests. When an attacker knows the CM MAC address, they can exploit a misconfiguration in the modem's response mechanisms to retrieve the WAN IPv6 address assigned to the device. This occurs due to inadequate access controls and authentication checks within the modem's network interface management system, allowing unauthenticated discovery of critical network addressing information. The vulnerability specifically impacts the IPv6 address discovery process rather than IPv4, highlighting a gap in security controls that affects modern network protocols. This flaw aligns with CWE-200, which addresses "Information Exposure," and represents a failure in implementing proper information hiding mechanisms that should prevent unauthorized access to sensitive network configuration data.
The operational impact of this vulnerability extends beyond simple information disclosure, creating potential pathways for more sophisticated attacks within the affected network infrastructure. Attackers who can discover WAN IPv6 addresses gain valuable intelligence for network reconnaissance activities, potentially enabling them to conduct targeted attacks against the modem or associated network services. The exposure of IPv6 addresses can facilitate various attack vectors including port scanning, service enumeration, and potential exploitation of IPv6-specific vulnerabilities. This vulnerability particularly affects environments where IPv6 is enabled and active, creating a persistent risk that remains exploitable as long as the vulnerable firmware versions are in use. The impact is amplified in enterprise environments where cable modems serve as primary network access points and where the exposed IPv6 addresses could provide attackers with direct routes to internal network resources.
Organizations should implement immediate mitigation strategies including firmware updates from Cisco to address the specific vulnerability in the affected devices, ensuring that all DPC3939 and DPC3941T modems are upgraded to versions that properly secure IPv6 address discovery mechanisms. Network segmentation and access control measures should be implemented to limit the potential impact if the vulnerability is exploited, while also monitoring for anomalous network activity that might indicate attempts to leverage this information disclosure. The remediation process should include comprehensive network inventory assessments to identify all affected devices and ensure that proper security configurations are applied. Security monitoring should be enhanced to detect unusual IPv6 address discovery patterns or attempts to query network configuration information, as outlined in the attack techniques documented in the MITRE ATT&CK framework under the reconnaissance and credential access categories. Regular vulnerability assessments and firmware update policies should be implemented to prevent similar issues from arising in other network infrastructure components and to maintain ongoing security posture against evolving threats.