Security Vulnerability Found

[porcupineyhairs]

Absolute Path Traversal due to incorrect use of send_file call

A path traversal attack (also known as directory traversal) aims to access files and directories that are stored outside the web root folder. By manipulating variables that reference files with “dot-dot-slash (../)” sequences and its variations or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system including application source code or configuration and critical system files. This attack is also known as “dot-dot-slash”, “directory traversal”, “directory climbing” and “backtracking”.

Root Cause Analysis

Passing untrusted input to flask.send_filecan lead to path traversal attacks.

In this case, the problems occurs due to the following code :
https://github.com/piaoyunsoft/bt_lnmp/blob/fa49519b04586a00e76c105e7ce1da36eadf6922/www/server/panel/BTPanel/__init__.py#L858

Here, the filename parameter is attacker controlled and is used as the filename passed to the send_file call. This leads to a path traversal attack.

Remediation

This can be fixed by preventing flow of untrusted data to the vulnerable send_file function. In case the application logic necessiates this behaviour, one can either use the flask.safe_join to join untrusted paths or replace flask.send_file calls with flask.send_from_directory calls.

References

• OWASP Path Traversal
• Python : Flask Path Traversal Vulnerability github/securitylab#669

This bug was found using CodeQL by Github