The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize '.../...//' (doubled triple dot slash) sequences that can resolve to a location that is outside of that directory.

Resultant

Implementation

Confidentiality
Integrity
Read Files or Directories
Modify Files or Directories
Bypass Protection Mechanism
Not properly neutralizing '.../...//' (doubled triple dot slash) allows attackers to traverse the file system to access files or directories that are outside of the restricted directory.

Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Implementation
Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."
Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
When validating filenames, use stringent allowlists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as CWE-23, and exclude directory separators such as "/" to avoid CWE-36. Use a list of allowable file extensions, which will help to avoid CWE-434.
Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a denylist, which may be incomplete (CWE-184). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (CWE-182). For example, the ".../...//" manipulation is useful for bypassing some path traversal protection schemes. If "../" sequences are removed from the ".../...//" string in a sequential fashion (as some regular expression engines and other algorithms operate) the string can collapse into the unsafe "../" value (CWE-182). Removing the first "../" yields "....//" and the second removal yields "../".

High

Implementation
Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

Suppose the product serves files from a specific "public" directory -- /home/product/public/ -- and has an algorithm that attempts to protect against common path traversal attacks. The algorithm works by sequentially scanning through a requested filename and removes each occurrence of "../" that it encounters, then appending the filename to the public directory.
If an attacker provides this filename:

../secret.dat

then the code would correctly remove the "../" resulting in the name:

/home/product/public/secret.dat

This request would fail, because secret.dat is not in /home/product/public/secret.dat.
The attacker could attempt to bypass this protection mechanism using this string:

.../...//secret.dat

The algorithm would remove the first occurrence of "../" to produce:

....//secret.dat

The algorithm would then find and remove the second (and final) "../" sequence, producing:

../secret.dat

At this point, the algorithm stops because it removed all "../" that appeared in the original string, but the algorithm has collapsed the original input into an unsafe value (CWE-182) that is still subject to path traversal.
The end result is:

/home/product/public/../secret.dat

Which the OS resolves to /home/product/secret.dat, a file that is outside the public directory.

The algorithm could be changed to use a built-in path canonicalization function that effectively removes "../" sequences, removes symbolic links, etc., such as realpath() in C. An alternate approach might be to run a loop that continues to remove "../" sequences from successive outputs until all suspect sequences are removed. However, relying solely on such a filter may be risky, since there may be sequences or characters that the filter is not covering for all environments.

CVE-2005-2169
chain: ".../...//" bypasses protection mechanism using regexp's that remove "../" resulting in collapse into an unsafe value "../" (CWE-182) and resultant path traversal.
https://www.cve.org/CVERecord?id=CVE-2005-2169

CVE-2005-0202
".../....///" bypasses regexp's that remove "./" and "../"
https://www.cve.org/CVERecord?id=CVE-2005-0202

File Processing

File or Directory

'.../...//'

SFP16
Path Traversal

Allowed
This CWE entry is at the Variant 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.

PLOVER
2006-07-19
Draft 3
2006-07-19

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Description, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2008-10-14
updated Description

CWE Content Team
MITRE
2008-11-24
updated Observed_Examples

CWE Content Team
MITRE
2009-07-27
updated Potential_Mitigations

CWE Content Team
MITRE
2010-06-21
updated Description, Potential_Mitigations

CWE Content Team
MITRE
2010-12-13
updated Relationships

CWE Content Team
MITRE
2011-03-29
updated Potential_Mitigations

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Relationships

CWE Content Team
MITRE
2014-07-30
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2017-11-08
updated Applicable_Platforms

CWE Content Team
MITRE
2020-02-24
updated Potential_Mitigations, Relationships

CWE Content Team
MITRE
2020-06-25
updated Potential_Mitigations

CWE Content Team
MITRE
2021-03-15
updated Potential_Mitigations

CWE Content Team
MITRE
2021-10-28
updated Relationships

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
2025-09-09
4.18
2025-09-09
updated Affected_Resources, Functional_Areas

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Common_Consequences, Demonstrative_Examples, Description, Detection_Factors, Diagram, Potential_Mitigations, Weakness_Ordinalities

Path Issue - Doubled Triple Dot Slash - '.../...//'