CVE-2025-26603: heap-use-after-free in function str_to_reg in vim/vim

Vim is a greatly improved version of the good old UNIX editor Vi. Vim allows to redirect screen messages using the :redir ex command to register, variables and files. It also allows to show the contents of registers using the :registers or :display ex command. When redirecting the output of :display to a register, Vim will free the register content before storing the new content in the register. Now when redirecting the :display command to a register that is being displayed, Vim will free the content while shortly afterwards trying to access it, which leads to a use-after-free. Vim pre 9.1.1115 checks in the exdisplay() function, that it does not try to redirect to a register while displaying this register at the same time. However this check is not complete, and so Vim does not check the + and registers (which typically donate the X11/clipboard registers, and when a clipboard connection is not possible will fall back to use register 0 instead. In Patch 9.1.1115 Vim will therefore skip outputting to register zero when trying to redirect to the clipboard registers or +. Users are advised to upgrade. There are no known workarounds for this vulnerability.

— MITRE