CWE-180: Incorrect Behavior Order: Validate Before Canonicalize
Description
The product validates input before it is canonicalized, which prevents the product from detecting data that becomes invalid after the canonicalization step.
Submission Date :
July 19, 2006, midnight
Modification Date :
2023-06-29 00:00:00+00:00
Organization :
MITRE
Extended Description
This can be used by an attacker to bypass the validation and launch attacks that expose weaknesses that would otherwise be prevented, such as injection.
Example - 1
The following code attempts to validate a given input path by checking it against an allowlist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/". The problem with the above code is that the validation step occurs before canonicalization occurs. An attacker could provide an input path of "/safe_dir/../" that would pass the validation step. However, the canonicalization process sees the double dot as a traversal to the parent directory and hence when canonicized the path would become just "/". To avoid this problem, validation should occur after canonicalization takes place. In this case canonicalization occurs during the initialization of the File object. The code below fixes the issue.
File f = new File(path);return f.getCanonicalPath();String path = getInputPath();if (path.startsWith("/safe_dir/")){}
return f.getCanonicalPath();
String path = getInputPath();File f = new File(path);if (f.getCanonicalPath().startsWith("/safe_dir/")){}
Related Weaknesses
This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined to give an overview of the different insight to similar items that may exist at higher and lower levels of abstraction.
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