While investigating Kodi, Tenable found two issues. After discussions with Kodi, we hesitate to call these vulnerabilities, but the issues are severe and unexpected enough that we felt an advisory should be issued.
Unauthenticated Remote Code Execution via HTTP Requests
By default, Kodi's HTTP server is disabled. However, when enabled, the server's default setting is to not require authentication. Kodi's HTTP server also supports the JSON-RPC API which allows remote users to control the local Kodi UI via HTTP requests. As such, a remote unauthenticated attacker can a install malicious package by sending mouse clicks and keystrokes via HTTP.
A proof of concept video follows. The attack is launched against Kodi 19.0 alpha. The script, available on our GitHub, enables third party packages, adds a new SMB source, and installs a package that configures a bind shell on port 1270. Note that this script would need to be modified for Kodi versions below 19 since the local UI is slightly different.
In response to this finding, the Kodi community has begun discussing requiring authentication on the HTTP interface. See the following pull request for more details: 17359.
Lock Screen Bypass
In an attempt to mitigate the above, we enabled the Master Lock feature. This feature enables a login screen in the local UI on start up. In theory, a user can only bypass this view via successful authentication. However, we found that simply sending an Input.Home JSON RPC message transitioned the local UI away from the login screen. From there an attacker could, more or less, do as they pleased. The video PoC above actually has the Master Lock enabled.
In response to this finding, Kodi updated their wiki to state the following about the Master Lock: Note: This feature only protects the Kodi interface from, say, curious children. It will not protect the content and settings files outside of Kodi from being accessed via the operating system. Also, it may be bypassed via the web interface or other add-ons and advanced Kodi features.
Disable access to the web interface. If you must use the web interface, ensure that password protection is enabled.
01/21/2020 - Tenable attempts to make contact with a Kodi developer.
01/21/2020 - The Kodi developer provides a more appropriate contact.
01/23/2020 - Tenable discloses to Kodi.
01/31/2020 - Tenable asks for an acknowledgement.
02/01/2020 - Kodi states, "Profiles are not designed to be a security feature/authentication" and provides feedback/follow up questions regarding the API over HTTP.
02/11/2020 - Kodi shows Tenable changes made to their wiki and a new pull request to handle HTTP authentication by default.
02/11/2020 - Tenable acknowledges.
All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.
Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers.
Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.
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