1686
Extended Description
A filter might only account for instances of special elements when they occur:
• relative to a marker (e.g. "at the beginning/end of string; the second argument"), or
• at an absolute position (e.g. "byte number 10").
This may leave special elements in the data that did not match the filter position, but still may be
dangerous.
Relationships
The table(s) below shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOr and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition, relationships such
as PeerOf and CanAlsoBe are defined to show similar weaknesses that may want to be explored.
Relevant to the view "Research Concepts" (CWE-1000)
Nature Type ID Name Page
ChildOf 791 Incomplete Filtering of Special Elements 1680
ParentOf 796 Only Filtering Special Elements Relative to a Marker 1687
ParentOf 797 Only Filtering Special Elements at an Absolute Position 1689
Relevant to the view "Architectural Concepts" (CWE-1008)
Nature Type ID Name Page
MemberOf 1019 Validate Inputs 2433
Common Consequences
Scope Impact Likelihood
Integrity Unexpected State
Demonstrative Examples
Example 1:
The following code takes untrusted input and uses a regular expression to filter a "../" element
located at the beginning 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.
Example Language: Perl (Bad)
my $Username = GetUntrustedInput();
$Username =~ s/^\.\.\///;
my $filename = "/home/user/" . $Username;
ReadAndSendFile($filename);
Since the regular expression is only looking for an instance of "../" at the beginning of the string, it
only removes the first "../" element. So an input value such as:
Example Language: (Attack)
../../../etc/passwd
will have the first "../" stripped, resulting in:
Example Language: (Result)
../../etc/passwd
This value is then concatenated with the /home/user/ directory:
CWE Version 4.14
CWE-796: Only Filtering Special Elements Relative to a Marker
CWE-796: Only Filtering Special Elements Relative to a Marker