Vim is an open source command line text editor. double-free in dialog_changed() in Vim < v9.1.0648. When abandoning a buffer, Vim may ask the user what to do with the modified buffer. If the user wants the changed buffer to be saved, Vim may create a new Untitled file, if the buffer did not have a name yet. However, when setting the buffer name to Unnamed, Vim will falsely free a pointer twice, leading to a double-free and possibly later to a heap-use-after-free, which can lead to a crash. The issue has been fixed as of Vim patch v9.1.0648.
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
The product calls free() twice on the same memory address.