CVE-2017-9139 in FH1202
Summary
by MITRE
There is a stack-based buffer overflow on some Tenda routers (FH1202/F1202/F1200: versions before 1.2.0.20). Crafted POST requests to an unspecified URL result in DoS, interrupting the HTTP service (used to login to the web UI of a router) for 1 to 2 seconds.
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Analysis
by VulDB Data Team • 10/01/2020
The vulnerability identified as CVE-2017-9139 represents a critical stack-based buffer overflow flaw affecting specific Tenda router models including FH1202 F1202 and F1200 devices. This security weakness resides within the web-based management interface of these networking devices, specifically manifesting when processing crafted POST requests to an unspecified URL endpoint. The affected firmware versions prior to 1.2.0.20 demonstrate insufficient input validation mechanisms that allow malicious actors to exploit this vulnerability through carefully constructed HTTP requests. The flaw operates at the application layer where the router's HTTP service fails to properly bounds-check user-supplied data before copying it onto the stack, creating an exploitable condition that can be leveraged for denial-of-service attacks.
The technical implementation of this vulnerability follows a classic stack-based buffer overflow pattern where insufficient bounds checking allows an attacker to overwrite adjacent memory locations on the program stack. When the router processes a malicious POST request containing oversized data payloads, the application fails to validate the input length against the allocated stack buffer size, resulting in memory corruption that causes the HTTP service to crash temporarily. The DoS condition manifests as a service interruption lasting approximately 1 to 2 seconds, during which time the web-based management interface becomes unavailable to legitimate users attempting to access router configuration settings. This timing characteristic suggests the vulnerability triggers an immediate service restart or process termination rather than a more subtle memory corruption that might persist longer.
The operational impact of CVE-2017-9139 extends beyond simple service disruption, as it represents a potential entry point for more sophisticated attacks targeting network infrastructure. Network administrators face the challenge of managing vulnerable devices in production environments where unauthorized access to router configuration could lead to complete network compromise. The vulnerability affects the web UI authentication and configuration interface, which serves as the primary management pathway for users to modify router settings, update firmware, or configure security policies. This creates a scenario where attackers could repeatedly exploit the DoS condition to maintain persistent access to network management functions while potentially masking more serious underlying security issues. The vulnerability aligns with CWE-121 stack-based buffer overflow classification and demonstrates characteristics consistent with attack patterns documented in the mitre ATT&CK framework under initial access and execution phases, where attackers can establish footholds through service disruption and subsequent re-access attempts.
Mitigation strategies for this vulnerability should prioritize immediate firmware updates to version 1.2.0.20 or later, which contain the necessary patches to address the buffer overflow condition. Network administrators should implement monitoring solutions to detect unusual patterns of HTTP service disruptions that might indicate exploitation attempts, while also considering network segmentation to limit the impact of successful attacks. The vulnerability underscores the importance of input validation and bounds checking in embedded systems, particularly those with web-based management interfaces that are frequently targeted by attackers. Additional defensive measures include implementing network access controls to restrict access to router management interfaces, deploying intrusion detection systems to monitor for suspicious HTTP traffic patterns, and establishing regular firmware update procedures to maintain device security posture. Organizations should also consider the broader implications of this vulnerability within their network infrastructure and implement comprehensive vulnerability management programs that include regular assessment of embedded devices and network equipment for similar security weaknesses.