"The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as .. that can resolve to a location that is outside of that directory." - Entry from the Common Weakness Enumeration
For more info visit <a href="https://cwe.mitre.org/data/definitions/23.html" target="_blank" rel="noopener noreferrer">CWE-23</a>