Checking if a file exists and then creating it in separate operations creates a Time-of-Check-Time-of-Use (TOCTOU) race condition. Between the
existence check and the file creation, another process or thread might create or delete the file, leading to unexpected behavior.
This race condition can cause several problems:
- Security vulnerabilities: An attacker might create a symbolic link pointing to a sensitive file between the check and
creation, causing your program to overwrite important system files.
- Data corruption: If multiple processes try to create the same file simultaneously, they might interfere with each other’s
operations.
- Unpredictable behavior: Your program might fail unexpectedly when the file system state changes between operations.
The root cause is that file system operations are not atomic by default. The gap between checking and acting gives other processes an opportunity
to modify the file system state.
What is the potential impact?
Race conditions in file operations can lead to security vulnerabilities where attackers exploit the timing gap to redirect file operations to
unintended locations. This can result in unauthorized file access, data corruption, or system compromise. In multi-threaded or multi-process
environments, these issues can cause unpredictable application behavior and data integrity problems.
