CVE-2017-9481 in DPC3939
Summary
by MITRE
The Comcast firmware on Cisco DPC3939 (firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST) devices allows remote attackers to obtain unintended access to the Network Processor (NP) 169.254/16 IP network by adding a routing-table entry that specifies the LAN IP address as the router for that network.
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Analysis
by VulDB Data Team • 11/02/2019
The vulnerability identified as CVE-2017-9481 affects Cisco DPC3939 cable modems running specific Comcast firmware versions, creating a significant security risk through improper network routing configuration. This flaw enables remote attackers to gain unauthorized access to the Network Processor component of the device by manipulating the routing table to direct traffic intended for the 169.254/16 IP network through the local area network interface. The issue stems from insufficient validation of routing table entries, allowing malicious actors to exploit this weakness without requiring physical access or elevated privileges.
The technical implementation of this vulnerability involves the manipulation of routing table entries within the modem's firmware to establish an incorrect route for the 169.254/16 network, which is typically used for link-local communication and should remain isolated from external routing. When an attacker adds a routing entry specifying the LAN IP address as the router for this network, the device's Network Processor becomes accessible through the unintended routing path. This creates a backdoor access mechanism that bypasses normal security controls and allows remote exploitation of the NP component, which typically handles critical network processing functions.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it provides attackers with a persistent entry point into the device's core networking infrastructure. The Network Processor is responsible for handling packet processing, network filtering, and routing decisions within the modem, making this access point particularly dangerous for network security. Attackers could potentially intercept, modify, or redirect network traffic, perform man-in-the-middle attacks, or establish further footholds within the network. The vulnerability affects devices running firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST, representing a significant risk to network infrastructure security.
This vulnerability maps to CWE-22 Improper Limitation of a Pathname to a Restricted Directory, specifically in the context of routing table manipulation and network access control. The flaw also aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS, as the routing manipulation could enable DNS-based attacks or DNS tunneling. Additionally, the vulnerability demonstrates characteristics of T1068 Remote Services and T1082 System Information Discovery, as attackers could use the access to gather system information and establish remote service connections. Organizations should implement network segmentation, monitor routing table changes, and apply firmware updates to address this vulnerability. The security implications require immediate attention as the flaw allows for persistent remote access to critical network infrastructure components without requiring authentication or physical access to the device.