The product 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.

Primary

Implementation
REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Integrity
Unexpected State

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.

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:

../../../etc/passwd

will have the first "../" stripped, resulting in:

../../etc/passwd

This value is then concatenated with the /home/user/ directory:

/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).

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.

my $Username = GetUntrustedInput();if (substr($Username, 0, 3) eq '../') {$Username = substr($Username, 3);}my $filename = "/home/user/" . $Username;ReadAndSendFile($filename);

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:

../../../etc/passwd

will have the first "../" filtered, resulting in:

../../etc/passwd

This value is then concatenated with the /home/user/ directory:

/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).

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

CWE Content Team
MITRE
2009-12-04
1.7
2009-12-28

CWE Content Team
MITRE
2010-06-21
updated Description

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2011-06-27
updated Common_Consequences

CWE Content Team
MITRE
2017-01-19
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Modes_of_Introduction, Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Demonstrative_Examples

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Weakness_Ordinalities