CWE-794: Incomplete Filtering of Multiple Instances of Special Elements
Description
The product receives data from an upstream component, but does not filter all instances of a special element 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
Extended Description
Incomplete filtering of this nature may be applied to:
- sequential elements (special elements that appear next to each other) or
- non-sequential elements (special elements that appear multiple times in different locations).
Example - 1
The following code takes untrusted input and uses a regular expression to filter "../" from the input. It then appends this result to the /home/user/ directory and attempts to read the file in the final resulting path. Since the regular expression does not have the /g global match modifier, it only removes the first instance of "../" it comes across. So an input value such as: will have the first "../" stripped, 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-23).
my $Username = GetUntrustedInput();$Username =~ s/\.\.\///;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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