Xunlei Accelerator (迅雷客户端) a.k.a. Xunlei Thunder by the China-based Xunlei Ltd. is a wildly popular application. According to the
company’s annual report 51.1 million active users were counted in December 2022. The company’s Google Chrome extension 迅雷下载支持, while not mandatory for using the application, had 28 million users at the time of writing.
I’ve found this application to expose a massive attack surface. This attack surface is largely accessible to arbitrary websites that an application user happens to be visiting. Some of it can also be accessed from other computers in the same network or by attackers with the ability to intercept user’s network connections (
Man-in-the-Middle attack).
It does not appear like security concerns were considered in the design of this application. Extensive internal interfaces were exposed without adequate protection. Some existing security mechanisms were disabled. The application also contains large amounts of third-party code which didn’t appear to receive any security updates whatsoever.
I’ve reported a number of vulnerabilities to Xunlei, most of which allowed remote code execution. Still, given the size of the attack surface it felt like I barely scratched the surface.
Last time Xunlei made security news, it was due to distributing a malicious software component. Back then
it was an inside job, some employees turned rouge. However, the application’s flaws allowed the same effect to be easily achieved from any website a user of the application happened to be visiting.
