QDir

Telegram Desktop Bug Deletes 800 GB of User Data Due to Spelling Checker Path Error

A Telegram Desktop update introduced a critical flaw that caused the application to recursively delete user folders containing up to 800 GB of data on Windows systems. The root cause traced back to an incorrect path construction for the custom dictionary file used by the lib_spellcheck library when Windows native spell checking was enabled. Due to a misplaced return statement in the code, the working directory path remained empty, leading Qt to interpret the path as the root-level C:\custom folder. The application then invoked QDir::removeRecursively on this directory, removing all accessible files while skipping locked ones. The bug affected releases 7.1.0 and 7.1.1 for approximately 66 hours before being fixed in version 7.1.2. Researchers used Process Monitor to confirm Telegram.exe was directly responsible for the deletion attempts. The incident highlights risks of combining recursive deletion functions with unvalidated path inputs in widely used applications.