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Fix Path Traversal Vulnerability #351
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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 The `os.path.join` call is unsafe for use with untrusted input. When the `os.path.join` call encounters an absolute path, it ignores all the parameters it has encountered till that point and starts working with the new absolute path. Please see the example below. ``` >>> import os.path >>> static = "path/to/mySafeStaticDir" >>> malicious = "/../../../../../etc/passwd" >>> os.path.join(t,malicious) '/../../../../../etc/passwd' ``` Since the "malicious" parameter represents an absolute path, the result of `os.path.join` ignores the static directory completely. Hence, untrusted input is passed via the `os.path.join` call to `flask.send_file` can lead to path traversal attacks. In this case, the problems occurs due to the following code : https://github.com/onlaj/Piano-LED-Visualizer/blob/6a732caa812c83a807c711f3d091af99209cae7b/webinterface/views_api.py#L970 Here, the `value` parameter is attacker controlled. This parameter passes through the unsafe `os.path.join` call making the effective directory and filename passed to the `send_file` call attacker controlled. This leads to a path traversal attack. ## Proof of Concept The bug can be verified using a proof of concept similar to the one shown below. ``` curl --path-as-is 'http://<domain>/api/change_setting?second_value=no_reload&disable_sequence=true&value=../../../../../../../etc/passwd"' ``` ## 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](https://owasp.org/www-community/attacks/Path_Traversal) * github/securitylab#669 ### This bug was found using *[CodeQL by Github](https://codeql.github.com/)*
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Thank you for your contribution and the detailed explanation of the vulnerability. I checked your pull request and it seems to work as expected, but PyCharm returns me a warning I assume that adding |
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@onlaj changes done! can you please request a GHSA advisory for this? |
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Sure, I can do it. Should I copy into the description what you wrote in the #350? |
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@onlaj Ecosystem means the primary language ecosystem to which the project belongs. In this case, since the bug is in python code, you may select As for severity, please select For CWE, please put |
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I made a draft and added you as collaborator, but I still don't fully understand what is it for. |
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@onlaj I have made a bunch to the draft advisory. PTAL. A CVE ID is used to identify a security vulnerability in a product. By issuing a CVE you allow the users of your software to be notified about a security vulnerability. If this software is used by other downstream libraries, a CVE would nudge them to upgrade to the patched version. Also sometimes, Github may even create a dependabot alert for users to auto-patch the bug. |
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Ok, I understand now. |
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@onlaj I don't know. You should be doing both. I think |
Fix Path Traversal Vulnerability

Fixes #350