The HTML\Browser plugin in SabreDAV before 1.6.9, 1.7.x before 1.7.7, and 1.8.x before 1.8.5, as used in ownCloud, when running on Windows, does not properly check path separators in the base path, which allows remote attackers to read arbitrary files via a \ (backslash) character.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.