CVE-2020-29656 in RT-AC88U Download Master
Summary
by MITRE • 12/09/2020
An information disclosure vulnerability exists in RT-AC88U Download Master before 3.1.0.108. A direct access to /downloadmaster/dm_apply.cgi?action_mode=initial&download_type=General&special_cgi=get_language makes it possible to reach "unknown functionality" in a "known to be easy" manner via an unspecified "public exploit."
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Analysis
by VulDB Data Team • 12/13/2020
The vulnerability CVE-2020-29656 represents an information disclosure weakness in the RT-AC88U Download Master component prior to version 3.1.0.108. This issue resides within the router's web interface administration system where unauthorized access to specific CGI endpoints can reveal sensitive system information. The vulnerability stems from inadequate input validation and access controls within the download master functionality, creating a pathway for attackers to exploit the system through direct URI access. The affected device, a consumer-grade router from ASUS, exposes administrative functions through predictable URL patterns that lack proper authentication mechanisms. This type of vulnerability falls under CWE-200, which specifically addresses information exposure through improper access control and insufficient validation of user inputs. The attack vector is particularly concerning as it requires no special privileges or complex exploitation techniques, making it accessible to adversaries with basic network reconnaissance capabilities. The vulnerability enables attackers to access language configuration data and potentially other system parameters through a straightforward HTTP GET request to the dm_apply.cgi endpoint.
The technical implementation of this vulnerability involves the router's web server processing requests to the /downloadmaster/dm_apply.cgi CGI script without proper authorization checks. When an attacker accesses the specific URI with parameters action_mode=initial, download_type=General, and special_cgi=get_language, the system returns information that should remain restricted to authenticated administrators. This behavior indicates a lack of proper session management and access control enforcement within the web application layer. The unspecified "public exploit" referenced in the description suggests that the vulnerability has been widely documented and potentially weaponized by threat actors, as the attack mechanism is described as "easy" and "known." The vulnerability exists because the web server does not properly validate whether the requesting entity has appropriate privileges to access the language configuration data, creating a path for information disclosure that could reveal system internals, configuration parameters, or other sensitive data that might aid in further exploitation attempts. This aligns with ATT&CK technique T1083, which covers the discovery of system information through direct access to system components.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with valuable reconnaissance data that can be used to plan more sophisticated attacks against the affected network. The disclosed information could include language settings, system version details, and potentially other configuration parameters that help attackers understand the device's capabilities and vulnerabilities. This information disclosure creates a foundation for additional exploitation attempts, including potential privilege escalation or further reconnaissance of the network infrastructure. Attackers could use the leaked information to tailor more effective attacks against the router's other services or to identify potential weaknesses in the overall network security posture. The vulnerability's presence in a consumer-grade router means that it affects home networks and small office environments where network security awareness may be limited, potentially exposing these networks to more serious threats. The lack of authentication checks for this particular endpoint represents a fundamental flaw in the application's security architecture, as it violates the principle of least privilege and proper access control enforcement. Organizations using affected devices should consider the potential for this vulnerability to be leveraged as part of broader attack campaigns targeting network infrastructure components. The vulnerability demonstrates the importance of proper input validation and access control implementation in web applications, particularly those running on embedded devices where security updates may be infrequent or unavailable.