Only Filtering Special Elements at a Specified Location
The software receives data from an upstream component, but only accounts for special elements at a specified location, thereby missing remaining special elements that may exist before sending it to a downstream component.
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.
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
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.
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:
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-22).
Weaknesses in this category are related to the design and architecture of a system's input validation components. Frequently these deal with sanitizing, neutralizing a...
Weaknesses in this category are related to the creation or neutralization of data using an incorrect format.
This view (slice) covers all the elements in CWE.
CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...
This view (slice) lists weaknesses that can be introduced during implementation.