CVE-2017-6631 in Set-top Box
Summary
by MITRE
A vulnerability in the HTTP remote procedure call (RPC) service of set-top box (STB) receivers manufactured by Cisco for Yes could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability exists because the firmware of an affected device fails to handle certain XML values that are passed to the HTTP RPC service listening on the local subnet of the device. An attacker could exploit this vulnerability by submitting a malformed request to an affected device. A successful attack could cause the affected device to restart, resulting in a DoS condition. Yes has updated the affected devices with firmware that addresses this vulnerability. Customers are not required to take action. Vulnerable Products: This vulnerability affects YesMaxTotal, YesMax HD, and YesQuattro STB devices. Cisco Bug IDs: CSCvd08812.
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Analysis
by VulDB Data Team • 01/11/2021
The vulnerability identified as CVE-2017-6631 represents a critical denial of service weakness within Cisco's set-top box implementations for the Yes television service platform. This flaw specifically targets the HTTP remote procedure call service that operates on affected STB devices, creating an exploitable condition that allows unauthenticated remote attackers to disrupt service availability. The vulnerability stems from inadequate input validation within the firmware's handling of XML data structures, particularly when these malformed values are processed through the HTTP RPC service interface. The affected devices operate within the local subnet environment, making them susceptible to exploitation from adjacent network positions without requiring additional authentication credentials or network privileges.
The technical exploitation mechanism of this vulnerability involves crafting and submitting malformed XML requests to the HTTP RPC service endpoint, which triggers an improper handling routine within the device firmware. When the affected STB receives these malformed XML values, the system fails to properly validate or sanitize the input before processing, leading to a cascading failure condition that ultimately results in device restart operations. This behavior demonstrates a classic buffer overflow or input validation failure pattern where the system does not adequately protect against malformed data inputs that exceed expected parameter boundaries or violate expected data formats. The vulnerability operates at the application layer of the network stack, specifically targeting the HTTP RPC service implementation that serves as the communication interface for device management and configuration functions.
From an operational impact perspective, this vulnerability creates significant disruption potential for service providers and end users alike, as the successful exploitation results in complete service interruption through device restarts. The DoS condition affects the availability of television services delivered through the Yes platform, potentially impacting thousands of subscribers simultaneously if exploited at scale. The local subnet requirement for exploitation means that attackers must be positioned within the same network segment as the target devices, limiting the scope of remote exploitation but not eliminating the threat entirely. This vulnerability affects specific hardware models including YesMaxTotal, YesMax HD, and YesQuattro STB devices, indicating a targeted impact across a defined product line rather than a broader platform vulnerability.
The remediation approach for this vulnerability involved firmware updates provided by Yes, which addressed the input validation deficiencies in the HTTP RPC service implementation. This solution demonstrates the importance of proper software patch management and the necessity of validating input parameters against expected data formats and structures. The vulnerability aligns with CWE-20, which covers "Improper Input Validation," and represents a specific instance where inadequate XML parsing and validation led to service disruption. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for "Endpoint Denial of Service" within the context of network service disruption. Security practitioners should recognize that this vulnerability highlights the critical need for robust input validation and sanitization practices in embedded systems and IoT devices, particularly those operating in customer premises environments where physical access may be limited but network exposure remains significant.