CVE-2017-9483 in DPC3939
Summary
by MITRE
The Comcast firmware on Cisco DPC3939 (firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST) devices allows Network Processor (NP) Linux users to obtain root access to the Application Processor (AP) Linux system via shell metacharacters in commands.
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Analysis
by VulDB Data Team • 11/02/2019
The vulnerability identified as CVE-2017-9483 affects Cisco DPC3939 cable modems running specific Comcast firmware versions, creating a critical privilege escalation pathway between distinct system components. This issue resides within the inter-process communication mechanisms between the Network Processor (NP) and Application Processor (AP) Linux systems, where improper input validation allows malicious shell metacharacters to traverse system boundaries. The flaw specifically manifests when NP Linux users execute commands that contain shell metacharacters, enabling arbitrary code execution that elevates privileges from standard user level to root access on the AP Linux system. This represents a fundamental breakdown in the security isolation between the two processors, where the NP environment should remain sandboxed from the AP environment.
The technical implementation of this vulnerability stems from inadequate sanitization of command inputs passed from the NP Linux environment to the AP Linux system. When shell metacharacters such as semicolons, ampersands, or command substitution operators are present in commands executed by NP users, these characters are not properly escaped or filtered before being processed by the AP system's shell interpreter. This allows attackers to inject malicious commands that execute with the elevated privileges of the AP Linux system, effectively bypassing the intended security boundaries between the two processor environments. The vulnerability operates at the command execution layer, making it particularly dangerous as it can be exploited through legitimate system interfaces without requiring additional attack vectors.
The operational impact of CVE-2017-9483 extends beyond simple privilege escalation, creating a persistent backdoor that enables attackers to maintain long-term access to the affected devices. Once root access is obtained on the AP system, adversaries can manipulate firmware updates, modify network configurations, install persistent malware, or establish covert communication channels. This vulnerability particularly affects cable modem gateways that serve as primary network entry points for residential and small business users, making them attractive targets for attackers seeking to establish footholds within larger network infrastructures. The exposure of root access to the AP system also allows for potential lateral movement attacks against connected networks and could facilitate more sophisticated operations such as man-in-the-middle attacks or data exfiltration.
Mitigation strategies for this vulnerability require immediate firmware updates from Cisco and Comcast to address the command injection flaw in the inter-processor communication mechanisms. Network administrators should implement network segmentation to limit access to these devices and monitor for unusual command execution patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in shell commands, and can be mapped to ATT&CK technique T1059.004 for command and scripting interpreter. Organizations should also consider implementing network-based intrusion detection systems to monitor for shell metacharacter patterns in command executions and establish baseline behavior for legitimate system operations to detect anomalous privilege escalation activities.
This vulnerability represents a classic case of insufficient input validation in multi-processor embedded systems where security boundaries are not properly enforced. The flaw demonstrates how interconnected systems in network infrastructure can create unexpected attack surfaces when proper sanitization and privilege separation mechanisms are not implemented. The security implications extend to broader concerns about embedded system security in network infrastructure devices, where the complexity of multi-processor architectures can introduce subtle but critical vulnerabilities. Organizations should treat this vulnerability as a critical threat requiring immediate remediation and consider conducting comprehensive security assessments of other embedded network devices to identify similar privilege escalation pathways that could be exploited in their environments.