CVE-2017-16959 in TL-WVR
Summary
by MITRE
The locale feature in cgi-bin/luci on TP-Link TL-WVR, TL-WAR, TL-ER, and TL-R devices allows remote authenticated users to test for the existence of arbitrary files by making an operation=write;locale=%0d request, and then making an operation=read request with a crafted Accept-Language HTTP header, related to the set_sysinfo and get_sysinfo functions in /usr/lib/lua/luci/controller/locale.lua in uhttpd.
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Analysis
by VulDB Data Team • 12/10/2019
The vulnerability CVE-2017-16959 represents a critical information disclosure flaw in the web interface of TP-Link wireless routers and networking equipment. This issue affects multiple device series including TL-WVR, TL-WAR, TL-ER, and TL-R models, exploiting a weakness in the locale handling functionality within the cgi-bin/luci web application. The vulnerability stems from improper input validation and sanitization within the uhttpd web server implementation, specifically in the locale.lua controller file that manages system information retrieval and modification operations.
The technical exploitation mechanism involves a two-step process that leverages the set_sysinfo and get_sysinfo functions to test file existence on the device filesystem. An authenticated attacker can initiate an operation=write;locale=%0d request followed by a crafted operation=read request with a specially constructed Accept-Language HTTP header. This sequence allows the attacker to probe the underlying filesystem structure and identify the presence of arbitrary files without requiring elevated privileges. The vulnerability is particularly concerning because it operates within the web interface context, meaning that an attacker who has obtained valid credentials for the device can leverage this flaw to gather sensitive system information.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with insight into the device's internal file structure and potentially exposes sensitive configuration files or system components. This reconnaissance capability enables more sophisticated attacks, including potential privilege escalation or further exploitation of other vulnerabilities within the device's firmware. The issue is classified under CWE-200 Information Exposure and aligns with ATT&CK technique T1083 File and Directory Discovery, as it allows adversaries to enumerate system resources and understand the target environment. The vulnerability affects devices running uhttpd web server software where the locale.lua controller is implemented, making it particularly relevant for embedded networking equipment that relies on this particular web framework implementation.
Mitigation strategies should focus on implementing proper input validation and sanitization for all user-supplied data, particularly within web application frameworks that handle locale and internationalization features. Network administrators should ensure that all TP-Link devices are updated with the latest firmware releases from the vendor, which typically include patches for such vulnerabilities. Access controls should be strictly enforced, limiting administrative access to trusted users only, and implementing network segmentation to reduce the attack surface. The vulnerability demonstrates the importance of secure coding practices in embedded systems and highlights the need for comprehensive security testing of web interfaces in network equipment, particularly when dealing with user-supplied parameters that can influence system behavior through indirect mechanisms.