CWE-797: Only Filtering Special Elements at an Absolute Position
Description
The product receives data from an upstream component, but only accounts for special elements at an absolute position (e.g. "byte number 10"), thereby missing remaining special elements that may exist before sending it to a downstream component.
Submission Date :
Dec. 4, 2009, midnight
Modification Date :
2023-06-29 00:00:00+00:00
Organization :
MITRE
Example - 1
The following code takes untrusted input and uses a substring function to filter a 3-character "../" element located at the 0-index position of the input string. It then appends this result to the /home/user/ directory and attempts to read the file in the final resulting path. Since the if function is only looking for a substring of "../" between the 0 and 2 position, it only removes that specific "../" element. So an input value such as: will have the first "../" filtered, resulting in: This value is then concatenated with the /home/user/ directory: which causes the /etc/passwd file to be retrieved once the operating system has resolved the ../ sequences in the pathname. This leads to relative path traversal (CWE-22).
$Username = substr($Username, 3);
my $Username = GetUntrustedInput();if (substr($Username, 0, 3) eq '../') {}my $filename = "/home/user/" . $Username;ReadAndSendFile($filename);../../../etc/passwd../../etc/passwd/home/user/../../etc/passwd
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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