CVE-2017-9480 in DPC3939
Summary
by MITRE
The Comcast firmware on Cisco DPC3939 (firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST) devices allows local users (e.g., users who have command access as a consequence of CVE-2017-9479 exploitation) to read arbitrary files via UPnP access to /var/IGD/.
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Analysis
by VulDB Data Team • 11/02/2019
The vulnerability identified as CVE-2017-9480 represents a critical file disclosure flaw within the Comcast firmware implementation on Cisco DPC3939 broadband routers. This issue manifests as an insecure direct object reference vulnerability that allows authenticated local attackers to access sensitive system files through Universal Plug and Play services. The vulnerability specifically affects firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST and demonstrates how improper access controls can lead to unauthorized data exposure. The affected path /var/IGD/ contains system configuration and operational data that should remain protected from unauthorized access. This vulnerability operates within the context of a broader attack chain where attackers first exploit CVE-2017-9479 to gain command-level access before leveraging this subsequent flaw to escalate their privileges and extract sensitive information. The UPnP service interface provides an entry point that lacks proper input validation and access control mechanisms, allowing attackers to traverse the filesystem and read arbitrary files that contain potentially sensitive configuration data, authentication tokens, or system parameters.
The technical implementation of this vulnerability stems from inadequate validation of user inputs within the UPnP service handling code. When legitimate UPnP requests are processed, the system fails to properly sanitize or validate the paths being requested, allowing attackers to manipulate the file access parameters. This flaw falls under CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal attacks. The vulnerability represents a classic case of insufficient access control where the system does not properly verify that the requesting user has appropriate authorization to access the specified files. The UPnP service interface appears to lack proper privilege checking mechanisms, enabling local users who have already gained command access through the preceding CVE-2017-9479 exploitation to bypass normal file system access controls. This allows attackers to read sensitive files from the /var/IGD/ directory that may contain system configuration information, user credentials, or other operational data that could be leveraged for further attacks.
The operational impact of CVE-2017-9480 extends beyond simple information disclosure to potentially enable more sophisticated attack vectors that could compromise the entire network infrastructure. Attackers who successfully exploit this vulnerability can obtain sensitive system information that may reveal network topology, device configurations, or authentication mechanisms that could facilitate lateral movement within the network. The extracted data could include router configuration files that contain network settings, firewall rules, or VPN configurations that provide attackers with insights into network security controls. This vulnerability also poses significant risk to the confidentiality and integrity of the affected network, as it allows attackers to access potentially sensitive operational data that could be used to plan more targeted attacks or to maintain persistent access to the network. The impact is particularly severe because it requires minimal additional privileges beyond what was already gained through the initial exploitation of CVE-2017-9479, making it a valuable escalation tool in attack scenarios.
Mitigation strategies for CVE-2017-9480 should focus on implementing proper access controls and input validation within the UPnP service implementation. Network administrators should immediately update firmware to versions that address this vulnerability, as Cisco has released patches to resolve the insecure file access issue. The solution involves implementing proper path validation that prevents traversal attacks and ensuring that all file access requests are properly authenticated and authorized. Organizations should also consider implementing network segmentation and monitoring to detect unauthorized access attempts to sensitive system directories. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1005, which involves data from local system storage, and T1071.004, which covers application layer protocols including UPnP. Security teams should implement network monitoring to detect anomalous UPnP traffic patterns and establish proper access control policies that limit the scope of file system access available through UPnP interfaces. Additionally, regular security assessments should verify that all network services properly implement input validation and access control measures to prevent similar vulnerabilities from being introduced in future firmware releases.