dpkg 1.15.9, 1.16.x before 1.16.14, and 1.17.x before 1.17.9 expect the patch program to be compliant with a need for the "C-style encoded filenames" feature, but is supported in environments with noncompliant patch programs, which triggers an interaction error that allows remote attackers to conduct directory traversal attacks and modify files outside of the intended directories via a crafted source package. NOTE: this vulnerability exists because of reliance on unrealistic constraints on the behavior of an external program.
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.