The flaws were found by Core Security, which described in an advisory a lengthy back and forth dialog with Lenovo starting in late October over the problems.
The affected application is SHAREit, which is designed to let people share files from Windows computers or Android devices over a local LAN or through a Wi-Fi hotspot that's created.
SHAREit is preloaded on Lenovo devices, including its ThinkPad and IdeaPad notebooks and other mobile devices. The vulnerable SHAREit versions are the Android 3.0.18_ww and Windows 2.5.1.1 packages, Core Security said.
On Windows, the vulnerable version of SHAREit had a hard-coded password that would allow anyone within range to connect to the application. The password was "12345678," and it couldn't be changed.
Incorporating a static password that can't be changed is considered a poor security practice.
Core Security found three other issues with the Windows version of SHAREit. A second software vulnerability could allow an attacker to view the names of files accessible to the SHAREit user, according to Lenovo's advisory.
Both the Windows and Android versions of SHAREit did not use encryption when transferring files. Files were transferred over HTTP, which means files are also vulnerable to a man-in-the-middle attack.
On Android devices, SHAREit didn't even bother to have a weak password for gaining access to its Wi-Fi hotspot: any device within range could join it, Core said.
Lenovo has made several changes to SHAREit. The updated version for Windows is 3.2.0 and 3.5.38_ww for Android. Windows users should see a prompt to update the next time the application is opened.
Both of the updated applications now have what Lenovo terms as a "secure mode." That mode asks SHAREit users to create a unique password before sharing files, preventing unauthorized devices from connecting. Secure mode will also encrypt file transfers using AES 256-bit encryption.
But users have to choose that mode, and Lenovo retains an "easy" mode. It was unclear if the easy mode retains the hard-coded password.