The tempfile.NamedTemporaryFile function is used to create temporary files with a specific name. Although this behavior is described in the os.path.join documentation it has led to numerous vulnerabilities in the past ( Cuckoo Sandbox Evasion, CVE-2020-35736). The var/lib components including the basepath are now ignored by os.path.join and an attacker can read any file without using a single. However, if the attacker passes the filename parameter /a/b/c.txt then the resulting variable file_path in line 3 is an absolute file path. to prevent a path traversal vulnerability. In line 4, the resulting path is checked to see if it contains a. In line 3, the resulting path is constructed from the user-controlled input filename using the os.path.join function. The following example shows this possible pitfall for developers.ģ file_path = os.path.join("var", "lib", filename)ħ return HttpResponse(f.read(), content_type='text/plain')
If one of the appended components starts with a /, all previous components including the basepath are removed and this component is treated as an absolute path. However, the function has a peculiarity that some developers are not aware of. The first parameter usually contains the basepath while each further parameter is appended to the basepath as a component. The os.path.join(path, *paths) function is used to join multiple file path components into a combined file path. Some developers are unaware of the difference between the versions and it has already led to a permission escalation vulnerability in Django ( CVE-2020-24583) and, in a very similar way, to a hardening bypass in WordPress. So, with Python > 3.6, the function os.makedirs has the same properties as the Linux command: mkdir -m 700 -p A/B/C. In Python 3.6, only the last folder C has permission 700 and the other folders A and B are created with the default permission 755. This implies that only the current user (owner) has read, write and execute rights for these folders.
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In line 2 of the following code snippet, the folders A/B/C are created with rwx- (0o700) permission. Its second parameter mode is used to specify the default permission of the created folders. The function os.makedirs creates one or more folders in the file system. It is not recommended to use assert statements for security-related checks but we do see them in real-world applications. In this example, the assert statement in line 2 would be ignored and every non-super user could reach the next lines of code. View.py 1 def superuser_action(request, user): If an assert is used, for example, as part of an authentication check this can lead to a security bypass. These are sometimes used by developers to assess certain conditions within the code. However, when code is optimized, all assert statements are ignored. Some pre-packaged Python applications are provided with optimized bytecode. It is especially effective when the application is used on a large scale or when there are few resources available. This allows the code to run faster and with less memory. Python offers the ability to execute code in an optimized way. If you are using any of these features, make sure to check your Python code! 1. By explaining each issue and its impact we hope to raise awareness and sharpen your security mindset. We chose pitfalls that we believe are less known in the developer community. In this blog post, we share 10 security pitfalls we encountered in real-world Python projects. Often it is only a very minor subtlety or detail that can make developers slip and add a severe security vulnerability to the code base. However, within Python, just like in any other programming language, there are certain features that can be misleading or misused by developers. Python developers trust their applications to have a solid security state due to the use of standard libraries and common frameworks.
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