CVE-2017-9479 in DPC3939
Summary
by MITRE
The Comcast firmware on Cisco DPC3939 (firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST) devices allows remote attackers to execute arbitrary commands as root by leveraging local network access and connecting to the syseventd server, as demonstrated by copying configuration data into a readable filesystem.
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Analysis
by VulDB Data Team • 11/02/2019
The vulnerability identified as CVE-2017-9479 affects Cisco DPC3939 cable modems running specific Comcast firmware versions, representing a critical remote code execution flaw that allows attackers to gain root-level system access. This vulnerability stems from insufficient input validation and authentication mechanisms within the syseventd server component, which operates on the device's local network interface. The flaw enables remote attackers with local network access to execute arbitrary commands with the highest privileges available on the system, effectively compromising the entire device. The vulnerability is particularly concerning because it requires minimal attack vectors to achieve maximum impact, as the attacker only needs network connectivity to the device's local network segment rather than physical access or complex exploitation techniques.
The technical implementation of this vulnerability involves the syseventd server's failure to properly validate incoming requests and authenticate command execution attempts. When an attacker connects to the syseventd server, they can leverage the lack of proper access controls to inject and execute malicious commands that run with root privileges. The demonstration of this vulnerability shows how attackers can copy configuration data into a readable filesystem, which serves as a proof-of-concept for the broader exploitation capabilities. This particular implementation follows patterns consistent with CWE-20 Improper Input Validation, where the system fails to properly validate or sanitize inputs received from external sources. The vulnerability also aligns with ATT&CK technique T1059.001 Command and Scripting Interpreter, as it enables attackers to execute commands directly on the compromised system.
The operational impact of CVE-2017-9479 extends beyond simple device compromise to potentially enable broader network infiltration and persistent access. Once an attacker gains root access to a modem, they can modify network configurations, redirect traffic, install backdoors, or use the device as a pivot point to attack other systems within the local network. This makes the vulnerability particularly dangerous in residential and small business environments where cable modems often serve as entry points to larger network infrastructures. The attack surface is further expanded because many users do not regularly update their modem firmware, leaving devices vulnerable for extended periods. The vulnerability also demonstrates the risks associated with embedded systems that lack proper security hardening, as the syseventd service operates with elevated privileges without adequate input validation or access controls.
Mitigation strategies for CVE-2017-9479 should focus on both immediate remediation and long-term security improvements. The most effective immediate solution involves updating the firmware to versions that address the syseventd authentication and input validation flaws, though this requires users to be aware of the vulnerability and actively seek updates. Network segmentation and firewall rules can help limit the attack surface by preventing unauthorized access to the modem's local network interfaces. Implementing network monitoring solutions that detect unusual syseventd activity or unauthorized configuration changes can provide early warning of exploitation attempts. Organizations should also consider disabling unnecessary services and ports on the device, particularly those that are not required for normal operation. The vulnerability highlights the importance of secure coding practices and proper input validation as outlined in the OWASP Top Ten and ISO/IEC 27001 security standards, emphasizing that embedded systems require the same security rigor as enterprise applications. Regular vulnerability assessments and firmware update policies are essential to prevent similar issues in other network infrastructure devices.