1688
The product receives data from an upstream component, but only accounts for special elements
positioned relative to a marker (e.g. "at the beginning/end of a string; the second argument"),
thereby missing remaining special elements that may exist before sending it to a downstream
component.
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 795 Only Filtering Special Elements at a Specified Location 1685
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:
Example Language: (Result)
/home/user/../../etc/passwd
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).
CWE Version 4.14
CWE-797: Only Filtering Special Elements at an Absolute Position
CWE-797: Only Filtering Special Elements at an Absolute Position