Improper Link Resolution Before File Access in the drag source staging path of the drag and drop protocol in kitty from 0.47.0 before 0.49.0 allows a program writing to the terminal to create files and directories at paths outside the st…

Overview

Improper Link Resolution Before File Access in the drag source staging path of the drag and drop protocol in kitty from 0.47.0 before 0.49.0 allows a program writing to the terminal to create files and directories at paths outside the staging directory, because subdir_data_for_drag() in kitty/dnd.c resolves a descendant of the staged item tree by constructing a path string and opening it with safe_open(path, O_DIRECTORY | O_RDONLY, 0) rather than by walking the tree one component at a time, so a client that declares two entries with the same name, the first a symlink whose target is an arbitrary absolute path and the second a directory, causes mkdirat() to fail with EEXIST, which the code ignores, and causes the subsequent path resolution to follow the symlink and return a directory descriptor outside the staging directory, which is then passed as the dirfd argument to add_payload() and used for every further create operation on that item and its descendants. Entry names are sanitised against path separators and dot components, but symlink targets are not validated. Files are created with O_CREAT | O_WRONLY | O_EXCL at mode 0644, so existing files cannot be overwritten, and directories are created with mkdirat() at mode 0755, so the attacker can create intermediate directories that did not previously exist. This results in the creation of files and directories at any path writable by the user running kitty, provided the symlink target is an existing directory.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.